Play Max Lines/Coins: If you're playing a slot with paylines, each one can win independently. That means the more lines you play, the more chances you have of winning. So you're better off playing 20 lines at $0.05 each than one line at $1.00. If you're playing with coins, more coins usually unlock the biggest payouts.
You first need to create an account at a licensed online casino. Then, deposit funds to your account through an accepted payment method. Choose the slots game you want to play, start it up, and set the size of the bet. Now, you just have to press the spin button to play one round.