All the material you need should be in the online training. You can always go back and view some videos again when it is not clear. When you are in the modeler and some things are unclear try hitting the F1 key. This should bring up a relevant help page. Very useful!
All other Mendix documentation should be available here: https://world.mendix.com/display/docs/Overview
Good luck and welcome to the community!
Just start building. When you run into something you do not know how to do, check the online documentation or watch a video again. Then if you still have problems potst your question in the forum. Most of the time you get answer real quick.