I need help understanding these things if you could help me

My friend buys and sells cars. He was talking to me about how it was a good deal and he didn't sign the title yet or if you get a dealers license you don't need to worry about that or going to sec. State...I'm not sure
Then he said its sitting outside so he put his plates on it but its uninsured bit at some point he will have to put PLPD on it.
Can someone give me a break down of how titles, plates and insurance works? When its needed, how a dealers license changes things, why you need a dealers license to buy and sell or why it helps.
That would be much appreciated thanks
