You should be able to position the cursor over the section that you want to start with and left click. The two blue markers should move there. When you hit play, it plays until you hit stop, then goes back to the same spot you positioned the cursor.
Make sure you don't hit the far left play button, because that starts the song from the beginning. It's the play button second from the left.
If you hover the cursor over the buttons, their function is described in a small yellow box.
There is something called rehearsal letters that you can program into the tab to specify a certain section, too. I never mess around with it, because it's just easier to left click.