At the beginning of your upkeep, look at the top card of your library. If it's a land card, you may put it onto the battlefield.
Putting a land onto the battlefield this way doesn’t count as playing a land. You’ll still be able to play a land during one of your main phases.
If the card is not a land card, or you choose not to put it onto the battlefield, it will stay on top of your library. In most cases, you’ll then draw it during your draw step.