Transport Tycoon Forums

what are they for?

First of all: Why did you post this on the graphics forum? This has absolutely no connection to it.
Second: Have you checked the OpenTTD wiki? The question you've asked gets answered over there.

Nightlies are daily builds that are compiled at 19:00 GMT (IIRC, it's 20:00 CEST). Waypoints are like stations but trains wont stop at them, you can use them to get more control on train's routes.