Welcome to osu!, player!

Here are a few resources to help you start your journey:

Beginner Training - hand-picked beatmaps to get you started.
Beatmap Packs - Get pre-packaged collections of beatmaps based around a common theme.
Beatmap Listing - Download some new beatmaps (songs) to play.
Frequently Asked Questions - find out the basics of the game.

A few quick tips while playing osu!:

Hit F8 in-game (or click "Show Chat" at the bottom-right corner of the screen) to join the global discussion. You can ask questions here if you run into any problems.
If you are having technical problems, make sure to check out the tech support forum, and search before asking!

Also make sure to check out the osu!academy video series (and subscribe if you wish!)