The game of NS is rather simple, and in that design, complex.
There are marines and aliens that wage war.
The marines all have the exact same upgrades except for specially given out items from the certain structures:
armory: gives welders, shotguns, and mines. can be upgraded to advanced armory.
welders: welds marines armor and structures health back to full, does next to nothing damage
mines: place them in a spot and if an alien runs over them they'll explode, killing any skulks in the near vacinity.
shotguns: good for delivering lots of damage quickly, effective against structures (100% damage) quick reloading abilty
advanced armory: gives out heavy machine guns and grenade launchers, required for protolab
heavy machine guns AKA hmg: good for killing lifeforms quickly and in masses. delivers 20 damage, or more, a bullet. bad for killing structures (50% damage) slow reloading ability
grenade launchers: worthless for taking out lifeforms, ability to bounce the grenade around corners, great for taking out structures (200% damage) VERY slow reloading ability
protolab: gives out jetpacks and/or heavy armor once jetpack tech and/or heavy armor tech is researched
jetpack: you can fly with the energy you use, your energy recharges but you cannot stay in suspended flight for very long, nor would you want to. good for moving about quickly and not deing.
heavy armor: a very heavy suit of armor, protecting your health from damage can be reparied by welders

other marine tech:
armor, weapon, and catpack upgrades requires armslab. Armslab requires armory
armor upgrade: armor is increased by 20 points for every standard issue marine (much more for heavy armor marines)
weapon upgrade: damage inflicted by turrets and weapons and grenades by 10 percent each level
catpack tech: make you shoot 2x faster, and run ~1.5x faster, requires comm dropping catpacks on the feild (like medpacks and ammo packs)
observitory allows research of phase tech and motion traking, as well as the ability to PING and BEACON.
phase tech: requires IP and OBS, allows building of phase gates
phase gates: allows instant transportation to other phase gates
motion tracking: allows marines to see uncloaked alien blips when aliens are moving
turret factory: allows marines to electrify resource towers and turret factories. allows turrets to be built in the vacinity of turret factory.
seige turret factory: upgraded from turret factory, allows seiges to be build in the vacinity of seige torret factory.

other:
PING: reveals everything in a certain area, decloakes everything in that area as well.
BEACON: brings all marines to marine spawn alive.

Alien tech and ext is MUCH simplier.
The alien team starts with one hive. Aliens respawn at hives. each new hive makes you respawn that much faster, and allows for new upgrades.
Aliens get three upgrade chamber choices, Sensory, Movement, Defence
Each chamber is bound to a hive, until that hive is destroyed. You cannot build different chambers once they are bound (even if you lose all of them) You can only build new types of chambers once the new hive is complete.
Alien upgrade chambers are most effective when you have three (or more) of them.
Sensory:
Cloaking: you are practicly inivsable, the faster you move, the more visable you are.
Scent of Fear:Allows you to see marines through walls.
Focus:Allows you to bite harder, but slower.
The sensory chamber itself makes all the aliens within the vicinity cloaked, and all marines to show up on scent of fear. (even if you don't have the upgrade)
Movement:
Clerity: Allows you to move much faster
Silence: Allows your footsteps to sound like a distance echo or not at all
Adrenaline: Allows you to regain your energy faster
Movements allow you to move to the nearest hive being attacked(built or unbuilt), and to move to the farthest distant BUILT hive. They also allow you to regain your energy quickly if you are in close vacinity.
Defence:
Carapase: Increases your armor, and therefore how many bullets you can take
Regen: Makes you regenerate your health faster
Redem: Makes you teleported back to the hive if your life drops too low. (does always work)
Defence chambers health other lifeforms and structures and themselves in the near vacinity.

Alien upgrades also come in the form of hive upgrades, and lifeforms.
Skulk: main job of ambushing marines in groups.
0 hive, bite:75 damage
1 hive, parasite: 10 damage, marine shows up on hive network until he dies, instant long range weapon
2 hive, leap: 80 damage (over the course of MANY seconds of leaping), allows you to move at a speed 2.25 times that of your typical waking speed
3 hive, xenocide: 170 damage (i think), does an explosion that can knock back marines, and seriously hurt/kill many of them.

Gorge: main job of building the alien economy
0 hive, spit: 30 damage, slow moving projectile
1 hive, heal: 5 damage, seriously heals many structures/lifeforms that are directly ahead of you
2 hive, bilebomb: 200 damage, increadble damage to MANY structures, no damage to any lifeforms
3 hive, web: 0 damage, creates a string between two walls that makes a marine unable to move or shoot or fly

lerk: main job of hurting groups of marines by gasing them or umbraing your hive
0 hive: bite: 75 damage, good against solo HURT marines that can't aim
1 hive: gas: 15 damage every couple seconds, GREAT for taking out marine armor, and medpacks
2 hive: umbra: makes all alien lifeforms in umbra take half damage from marine bullets
3 hive: primal scream: makes all alien lifeforms in a limited area around the lerk regen energy faster, and hit twice as fast.

fade: main job of harssing marines and supporting skulks against groups of marines
0 hive: swipe: 80 damage, main attack of fades
1 hive: blink: allows fade to move at leap speed (4x as fade typically moves) for the cost of energy
2 hive: metabole: increases fades energy and health
3 hive: acid rocket: damage 25 hp 50 armor, GREAT for taking down heavies armor

onos: anti heavy, and tank
0 hive: gore, 80 damage
1 hive: devour, you eat a marine and gain little health from him until he dies (good for killing heavy armor marines
2 hive: stomp, all none jet pack marines in stomp area (line in front of onos) are unable to move or shoot
3 hive: charge, allows the onos to run very fast and do some damage as well


ok, more complex then basic. BTW where you are is told on your hud (lower right/left side (unsure which side))
obviously 2 hives improve alien strength greatly (new upgrades, and new weapons/skills) just think, if you could always take half damage and fight half dead marines, all the while regaining your health at nine times the speed. of before, (umbra + gas + dcs + regen upgrade + metabole) hives are very important too aliens, nodes are very important to marines. (killing 1 alien node takes longer to do, but is more benifical than building one of your own (typically) but only because aliens don't need as many nodes as marines, so losing one is like losing 2 marine nodes)