My six month old still doesn't sit?

Hi im in college im a first time mom so i really don't know any tips on how to teach my son to sit and not fall back or onto his face. He tries to sit up but he can not quite get up. He also does not know how to hoist himself up when hes on his belly( like to be in a crawling position) Can anyone give me any tips? everything i have read said most babies should be doing these things at this age, I know all children are different BUT I would love to try and help him if i can :] thank you