Depends on what you want to do. Want to be in the thick of the fight? Be a fighter or barbarian. Want to be more subtle in your actions? Be a rogue or monk. Like supporting others and keeping everyone alive, while occasionally getting a few licks in? Be a cleric, paladin or a bard. Want to stalk the woods and fight from a distance? Be a ranger or druid. Interested in casting spells? Be a wizard, sorcerer or warlock. More interested in the social aspects of the game — schmoozing with folks, gathering information and so on? Bard or rogue.
Fifth edition has a lot of options, though. Eldritch knights are fighters who can cast a few wizard spells, for example. Bards are good if you're interested in a swashbuckling sort of character, swinging from chandeliers waving a rapier and casting spells.
I would suggest don't worry about the rules too much at this point, though. Create a character concept that appeals to you and get with your dungeon master to craft the class and race options to get a character reasonably close to your idea.