Osu! Main Website

This website is where all the magic happens. You download beatmaps here and you can view stats here. Your best performances and recent plays all on here.

https://osu.ppy.sh/

The beatmaps tab is where you download all your playable maps. You also have certain filters to help locate specific songs you are looking for: Recommended Difficulty, Ranked & Approved(Maps where you get PP)
The rankings tab are the world wide rankings. All different game modes have their own Performance Rankings and these can be even filtered down to country rankings.