Hi Sheila!
There are indeed boats that will carry guests from one end of Epcot's World Showcase to the other. They operate throughout the opening hours of the World Showcase so they won't begin until at least 11am. These boats generally run two routes although I have been in the park before when only one boat is running so you will need to check on this when you arrive.
As you approach the World Showcase you will find the first boat launch area located on the right side or Canada side in the World Showcase Plaza. This is the area just behind the shops. This right side boat will take you across the water and will dock in the Morocco Pavilion dock.
The other boat will have a launch site located on the left side of the World Showcase Plaza and that boat will dock at the other end in the Germany Pavilion area. These boats will run back and forth taking guests in both directions.
You could certainly walk as far as you would enjoy into the World Showcase and then catch a boat back to the World Showcase Plaza.
If you wish to take a Friendship boat to the Hollywood Studios park you can also exit the World Showcase at the International Gateway and find a boat launch there. These
Boats will transport you to the Yacht and Beach Club dock, the Swan and Dolphin resorts, the Boardwalk resort and Hollywood Studios park. You are more then welcome to enjoy this boat ride and do a complete circle and return back to Epcot.
Enjoy your days in the parks!