You have trial for 24 hours. If this is not enough, providing credit card details at Spotify.com your another trial will be one month! No money will be charged with trial. You can cancel at any time and use your trial to the end.
Premium is 9,90 € for month and will be cahrged after trial if you want to use service. Even if you keep your subscription, trial time is total free. You will be charged for another month if you do not cancel before.