Urban Evolution's effect allows you to play an additional land during your main phase. Doing so follows the normal timing rules for playing lands. In particular, you don't get to play a land as Urban Evolution resolves; Urban Evolution fully resolves (and you'll draw three cards, perhaps including a land you'll play later) first.

The effects of multiple Urban Evolutions in the same turn are cumulative. They're also cumulative with other effects that let you play additional lands, such as the one from Rites of Flourishing.

If you somehow manage to cast Urban Evolution when it's not your turn, you'll draw three cards when it resolves, but you won't be able to play a land that turn.