First off, Welcome to NS. Second, you should try reading the guide first before posting in the forum. Third, kuz im in a good mood, ill do you a favor, here is a breif desc:
Marines:
LMG - pistol - knife on startup
can replace LMG to HMG, shotgun, or grenade launcher
Can also have jetpack or hevy armor (not both)
skulk -can walk on walls
bite - main attack, very powerful
parasite - marks an enemy structure or player on hive sight so everyone can see
leap - a long jump, does little damage, more of a speed advantage
xenocide - explosive suicide, area effect
gorge (fatty) - can build structures
spit - main defensive weapon, weak
heal spray - heals players and structures
bile bomb - does heavy damage against buildings ONLY
web - causes marines to stop and unable to fire weapons

lerk - flight
bite - a little less powerful than skulk's but faster
spores - gas that does damage agains light armor marines ONLY
umbra - blocks 1/2 bullets if your inside the cloud
primal scream - increases speed and energy recovery for all aliens in vicinity

fade can teleport (aka "the bladed messiah" by shockwave)
swipe - powerful attack
blink - teleportation
metabolize - health regen
acid rocket - acid projectile with splash damage

onos - juggernaught
gore - powerful main attack
devour - eat a marine and gain health from him until hes fully digested
stomp - stops marines for an amount of time in a straight path in front of you
charge - attack based on amount of touches, last until energy is out.
there you go, look around the rest of the forum for more info.