I was looking to understand how the baking works in Blender, since I have a few objects that will need to use a single texture at the end of the project. I have found these 2 videos working the best for my little brain. Note, that in both cases Cycles Render is used. It will work with other, but some steps will be slightly different. That should be easy to do once you get the workflow. This first one deals with baking single texture for multiple objects, where initially each object has its own texture. It uses the Blender built-in addon, Texture Atlas. The second one deals with baking single texture for single object using multiple materials. It does not need Texture Atlas addon.
