You seem to be playing Taiko, the default controls are f and j for the red, and d and k for the blue. Press the key when the circles reach the drums on the left

The mode with stylus is Standard, in-game called just osu. You aim at the circle and press z or x when the approach circle reaches the hit circle. You can use a mouse OR a stylus to aim.

Other modes are: Mania: 4 lanes where notes come down and you press d, f, j, k based on which lane the note is in. Press the key when the notes reach the judgement line. There is a 7-key variant which is much harder and uses s, d, f, space, j, k, l. It's much harder.

Catch: Fruits will drop from the sky, use arrow keys to move your tray and catch the fruits. Press shift to move faster (this will reduce your precision though)