Scaretiller's ability is a triggered ability, not an activated ability. It doesn't allow you to tap it whenever you want; rather, you need some other way of tapping it, such as by attacking.

If Scaretiller becomes tapped while casting a spell or activating an ability, that spell or ability resolves after Scaretiller's triggered ability has resolved.

Neither mode of Scaretiller's ability counts as playing a land. It can put a land card onto the battlefield even if you've already played your land for the turn, and even if it's not your turn.