You need to select a bet amount and then press the spin button to start the slot machine. Many slot guides also note that you can adjust paylines or use auto-spin before you begin, depending on the machine or app.

Quick steps

  1. Set your bet.
  2. Choose paylines or other options if the machine offers them.
  3. Tap or click spin.
  4. Wait for the reels to stop and check the result.

Extra note

Some slots automatically set a default bet when you load the game, so it’s smart to double-check it before spinning.

If you meant the phrase literally

If you were asking what physical thing is needed, the answer is just the machine’s spin button or lever, plus an active bet on the game.

TL;DR: Set your bet, then hit spin.