TL;DR
Rails isn't difficult to learn, but you must have rock solid knowledge of OOP
Rails has been created to be easy to use / up and running without much effort. The problem here (IMHO) is that you should start using a framework only after having learnt how to program without it.
Spend some time learning how OOP (Object-Oriented Programming) works. Write down some plain Ruby code and experiment how Ruby works (use IRB from Terminal)
Some good starting points: