A spinner is a hit object in osu! which takes up the entire play area. To clear a spinner, hold down your specified mouse/keyboard-button (or keep the pen onto the tablet). From there, use the mouse (or pen) and spin the spinner in a circular motion (in either direction) until the spinner circle grows outwards completely. A Clear notice will appear to indicate that the spinner was completed. If the spinner was cleared early, continue spinning to collect an extra score bonus and gain some health back.
The outer white circle shows how much time left to complete the spinner. This circle will turn red to notify that time is almost out. Older beatmaps, using skin version 1.0, will have a meter/gauge to indicate how close the player is to clearing the spinner. The small box below the spinner shows spins per minute. The number inside that box translates to the number of spins possible, if to continue to spin the spinner at that speed for one minute. If mouse/keyboard-button was released (or pen did not touch the tablet) early during the spin, the spinner will stop reading the spin.