There is some info on the wiki but its somewhat out of date. I did start trying to update it but haven't had much time recently. Anyway, a very quick overview:
Lasers: standard energy weapon, range up to ~ 1 million km at very high tech and increases with weapon size, damage falls off with range, needs power, can be turreted, good armour pentration
Particle Beams: range is similar to lasers but all sizes have same range, damage constant over range, needs power, cannot be turreted
Mesons: shorter range than lasers, range increases with weapon size, only ever does 1 point of damage but always ignores shields and armour, needs power, can be turreted
Plasma carronade: very short range, very damaging, needs power... not sure if can be turreted, I've never used them!
Microwave: short range, can disable sensors and fire control on target, and does 3x damage to shields, needs power, cannot be turreted
Missiles: very long range (10s to 100s of millions of km), can be shot down, missiles must be manufactured and loaded onto ships individually
Gauss Cannons: rapid fire low damage, does not require power, can be turreted. very useful for point defense
Railguns: does more damage than lasers but splits it into 4 chunks meaning that armour penetration is less, requires power, cannot be turreted
CIWS: an anti missile system which uses your gauss cannon, sensor and turret tech to determine capability. will automatically engage missiles about to hit the ship on which it is installed.
Regarding the particle beam/torpedo thing, they used to be torpedos but are now beams. Some of the descriptive text has not yet been changed