Choosing which page opens first
When you run a project, one page loads first. Setting that page deliberately saves you from clicking through the site on every test run.
Set it on the file
Right click the page you are working on and choose the option to set it as the start page. The next run opens that page directly.
Why it speeds you up
Testing a deep page usually means signing in, navigating and filling a form before you reach the screen you care about. Starting on the page itself removes all of that friction, at least while you are building it.
Remember the visitor. Before you finish, run the project from the real first page and walk the whole path. A page can work perfectly on its own and fail when a visitor arrives with no session.
Once the right page opens, use the debugger to follow the code, and restore any window you have hidden along the way.