The galaxy has a million different types of starship weapons, but they can be grouped into the following broad categories based on their role and performance:

Torpedoes: Torpedoes are massive guided missiles. How massive depends on the size of the vessel - battleships generally have bigger fish than destroyers for example. Range also varies - it's a compromise thing between speed, range, ECM/ECCM, armour/shielding and payload. The exact configuaration also depends on the role of the vessel. Destroyers will tend to have torpedoes with lower ranges than cruisers for example; they are positioned in the screen and their role is to dart in using their superior speed to deply short-range but powerful torpedoes against larger vessels. Ships defend against topedoes with shields and armour, but their best option is shooting them down with batteries, turrets - or small craft. This isn't as easy as it sounds - torpedoes are small (relative to space), fast and frequently well protected.

Nova cannon: The 'nova cannon' is a variation of the torpedo concept. It uses a massive spinal-mounted massdriver (preventing all but the largest ships from carrying them) to accelerate torpedo-like munitions at cee-fractional speeds. The warhead has a limited capacity to manoeuvre during its final attack run. The end result is a weapon with extreme range, mediocre accuracy, and incredible damage potential. Practical experience has shown it to be less effective against fleet ships, but invaluable for taking on orbital defences.

Lances: Lances are heavy long-range weapons, often energy-based. They constitue the primary long-range firepower of most capital starships from frigates and up. They are relatively slow-firing are require enormous amounts of energy. As with all starship weapons they come in a variety of shapes and sizes, from the smaller demi-lances used on smaller vessel to huge batteries of macro-lances mounted on the biggest battleships. On smaller ships lances are often spinal-mounted (i.e. firing only in a narrow cone along the ship's axis), but larger vessels (cruisers and above) favor massive external turrets that provide a greater arc of fire. The best defence against lances is avoiding getting hit; range, speed, size, evasive maneuvers, ECM - anything that can prevent accurate lance fire. Shields are also useful, especially when combined with the above countermeasures. Armour is less useful - the power of lances is such that even heavy armour can be breached. As a result many captains are reluctant to waste lance fire (and energy) on smaller vessels.

Bombardment cannon: The so-called bombardment cannon is a lance-like weapon system built around a powerful massdriver system. It's range and accuracy is limited compared to true lances, but it can inflict horrendous damage on both ground and space targets (space stations and weapon platforms are especially vulnerable). In the Imperium this weapon is almost exclusive to Marine strike cruisers and battle barges.

Batteries: This is the least homogenous weapon category, including massdriver-launched hypervelocity rockets, guided missiles, energy weapons and projectile weapons. Batteries are primarily short-to-medium range weapons. As a general rule missile weapons have the longest ranges, followed by energy weapon and finally projectile weapons, although this breakdown is far from universal. Another tendency is that short-range weapons are more lethal than long-range weapons, a fact aggravate by reduced response times for the defenders at close quarters. Larger ships have their batteries located inside the primary hull, giving excellent protection for the weapons but reducing fire arcs (this is why most cruisers and battleships favour 'broadsides' at medium-short ranges). Smaller vessels have no such luxury and many mount their batteries in multiple turret-like structures to maximize firepower (but sacrificing almost all armour protection).

Turrets: Turrets are light (in starship terms, these weapons would make short work of even heavy ground-based armoured vehicles) short-range weapon systems optimized for defending against incoming torpedoes and small craft. In a secondary role they can defend against battery fire, but unless the range is very great their chances of intercepting incoming fire is low. Typical weapons include multi-barreled heavy autocannon, megabolters, rapid-fire lascannon and tri-focused plasma cannons. Other turret options include various variations of particle field projectors ('sand-casters') that distrupt incoming energy barrages.

Fighters: Fighters are small craft that have limited ability to damage capital voidships. Their role is to destroy other fighters, bombers and other small craft, plus intercept torpedoes and protect own bombers/small craft/torpedoes  from interception. Against unshielded capital ships they can inflict damage against surface fixtures - turrets, auspex clusters, external batteries, etc. - but lack the firepower to pierce heavy armour. Some fighters can operate in athmospheres while others are optimized for space combat. Fighters operate in formations called flights (small), squadrons (medium) and wings (large). Fighters have great speed and maneuverability, but limited endurance and must be based on ships, space stations or on planetary surfaces.

Bombers: Bombers are large fighters. They have more protection, but less speed and manuverability. They are designed to dart in against capital ships and deliver their payload of ordnance. Unlike fighters they have the capacity to threathen even large vessels, such as cruisers and battleships, and they are a great threath to anything from raiders to frigates. Survivability against concentrated battery fire is limited, so they must select their attack vectors with care. Their chief enemy is enemy fighters - without escorting fighters they are nearly helpless. Bombers are otherwise similar to fighters.

Boarding craft: Imperial Navy vessels do not usually carry much in the way of boarding craft. Boarding a multi-million tonnes vessel with crews running from thousands to tens of thousands (or more) requires very specialized troops to be successful. Space Marine craft on the other hand are well equipped for boarding - correctly handles a Marine Strike Cruiser carrying a Company of Astartes can cripple a cruiser-sized vessel. Chaos and some xenos (orks for example) are also fond of boarding. There are three basic types of boarding craft: Boarding torpedoes, small craft, and teleporters.

Boarding torpedoes allow boarders to attack fully functioning enemy vessels - they can penetrate shields and starship hulls (but not heavily armoured sections). Range is short and it is not advisable to launch torpedoes against ships with heavy turret coverage. Boarding torpedoes are often used by Space Marines.

Small craft includes assault shuttles and other transports. They are best used for taking crippled ships, ships that have surrendered, and vessels without capital scale turrets and batteries (i.e. freighters and transports). The Space Marine Thunderhawk is perhaps the most well-known craft of this type; a boarding vessel that can performs as a fighter, bomber, dropship and gunship as needed.

Teleporters are the most effective - but unfortunately most fickle - boarding system. It allows attackers to strike deep into enemy vessels, taking key areas without the need for long advances through enemy territory. Space Marines are the only regular users of assault teleporters in the Imperium.