Hello there, and welcome to osu!. Let's learn how to play.
So, osu! is a game about circles. When the approach circle touches the edge of the inner circle, that's your cue to click it. You can then earn more score by accurately syncing your clicks to the music. Give these circles a try.
Sliders build on circle mechanics. Click on the start position just like a circle then keep holding the mouse button as you follow this ball at a predetermined speed along the track. If a slider than has a reverse arrow, you need to follow them backwards too. So, try some of these yourself.
The spinner is the simplest object type. Just hold your mouse button and spin your cursor around the center of the screen as fast as you can. Now you try.
And that covers the basics of osu! gameplay. To see if you've really getting the hang of this, try playing the song to its end and pay attention to your accuracy. If you see anything below 300 here, that means you're clicking beats too early or too late. Also you can click with the "x" and "z" keys on your keyboard. Good luck, and have fun playing osu!.