As much as i love pressing f for fun, real advice would be listen to Urcscumug - he pointed out some valuable info, also take a bit of time to watch some good players, try to learn what they do and ask why they do it if it looks really confusing, like running back from a wall instead of just running around it.
Imo the best way to learn weapons is to get as good as you can with a rifle/dretch if you are good with the free classes you will always have evos/credits and can upgrade at will.
And the biggest point would be if your new, do everything you can not to die, if your s1 and you get below 94 hp, run back to base grab 100hp + medkit. Always buy helmet and larmour, and as an alien, try not to treat dretch like a suicider, when you get low like every other alien just wait for your hp to return. If you follow that part of how to stay alive and if you use basic weapons you will end up with alot more credits/evos, which then you should also share to good, known players when there low and they will share you back, eventually you will just join games and instantly be given evos/credits as you are known as a friendly player.
: )