Hi I'm also relatively new but I can give you basic help.
- To switch to another branch use "Checkout". Just click on your branch and then on the button "checkout" at the top.
UPDATE 12.01.2016:
The bold line is the current branch.
You can also just double click a branch to use checkout.
- Your first answer I think depends on the repository you use (like github or bitbucket).
Maybe the "Show hosted repository"-Button can help you (Left panel, bottom, right button = database with cog)
And here some helpful links:
Easy Git Guide
Git-flow - Git branching model
Tips on branching with sourcetree