SageMathCloud is by far the best way to use Sage for new users. To help you get things sorted out there are many freely available video tutorials. Each is a short, focused demonstration of how to do something useful with SMC.
To avoid becoming language-dependent these videos are silent. This is better for Sage’s global audience, and I like to pretend that Buster Keaton is the one moving the mouse.
(I will fill these in as they get made.) The following videos all focus on using Sage through the SageMathCloud service.