The trail heads for Laguna Torre and Laguna de Las Tres are located on the outskirts of the town. On the bus ride into town, you'll stop at the Parks visitor centre and go the rules/regulations. They'll also give you a map and it will tell you where the trail heads are.
It is often advised that when you do the Laguna de Las Tres (Fitz Roy) trek, you take a mini bus to Hosteria El Pilar and hike to the base from there, then you can hike back to town from Fitz Roy. This just saves you back tracking and rehiking the same route.

