It means a quirky, odd, eccentric, or unusual person. In Ireland it usually means that you like the person or you enjoy the quirk or eccentricity. We also use it for small children who show a lot of personality or who are cheeky.

It means that he has a unique personality.

This phrase is often used as a euphemism. If you want to refer to someone who is rather strange, but you want to say something polite-sounding about them, you'd say 'He's a bit of a character'. And as Richie says, teachers would generally describe a cheeky or even badly behaved or difficult child as being 'a character'.

he has a kind of character distinguished from others. i think it's used to praise someone