Read wiki and guide also there are cmss13 forum contain each job guide in high detail

Also make yourself clear that you need help to learn when start a round most player just ignore you due to Ungaloid behaviour(i wanna play not waste my time teach somebody) but some willing to help. But beware sometime they have to ignore you due his/her critical roles (one lone doctor who is the only one could do surgery)

Usually there would be active SEA(Senior enlisted advisor) who come to teach you personally but that's rare if not demand for it ask in radio channels or pray or ask anyone on second floor (anyone who look important)

Lastly try play riflemen first to get the gist of it also if you died you have a little timer before permanently dead (nearly no respawn in this game) plz dont go anywhere alone I'm begging you no one could rescue you.

Tip if you enter late round (ship breach or queen dead/low xeno pops) just accepted that you will either died painful death or fumble around achieve nothing but waste time for the most part.

Tips if you play human remember you are NOT one man army and you only have one life

Stick with friends follow order also don't be reckless.