This phrase means that a person has several positive characteristics, like being smart, attractive, etc.

You usually say this to someone who's feeling bad about themself, or about someone who's had some kind of failure.

Some examples:

He's got a lot going for him.

Why would someone with so much going for him waste it all by dropping out of school?

There are some other phrases which sound similar, but have different meanings:

"You have a lot going on" means that a lot of stuff is happening in someone's life.

"You're going through a lot" means that a lot of difficult stuff is happening to someone.