Getting to Yelapa is by way of Puerto Vallarta. From PV, you need to take a water taxi to Yelapa. In Yelapa it is all you all the time, unless you need a horse to take you somewhere.
Everything is within walking distance. Or you can kayak across the bay. It is a very small village and everything is close by. Just make sure to have comfortable, water-friendly footwear !!
If you're visiting Yelapa just for the day, go ahead and buy a return ticket. However, if you're staying in the village, just get a one-way. When you finally do return to Puerto Vallarta or Boca, buy another one-way ticket. That way, you're not stuck waiting for the same boat that brought you to Yelapa, and you can do business with the next panga boat that comes along.
Sometimes, two one-ways are cheaper than the tourist round trip fare, anyway.
Make sure you purchase a return ticket at Boca de Tomatlán or wherever you get on a water taxi to go over to Yelapa. Don't lose your ticket and then also don't miss your return water taxi back! The last return taxi of the day is typically at 4pm. You wouldn't want to wind up having to pay double or who knows how much just to get back! Buy or Beware! ;)