The USGS has a very good collection of videos on YouTube about their various products. The best place to start is to view the short intro to version 6 data. You will learn about the various products, where to find data, how to use the LP DAAC site.
This first introductory video will be followed by more in-depth videos of various products. These are their “Getting Started with…” videos covering Surface Reflectance, Temperature, Vegetation Indexes, etc.