The following includes a list of tools for learning economics. They include the level of difficulty.
Khan Academy Has excellent introductory material. Salman does a great job of explaining the principles you need to know in economics. Level (Basic). Requirements (Algebra, Calculus)
MIT's intermediate Macro. MIT's undergraduate courses compare to some graduate level courses. Great way to learn more without getting too technical. Level (Intermediate). Requirements (Micro, Game theory, Calculus, optimization)
Queen's University. Provides a course on some intermediate macroeconomics. It uses gentle dynamic optimzation , introduction to growth, business cycles, and consumptions. Level (Intermediate). Requirements (Optimization, calculus)
MIT's 1st year Macro Sequence- This is as hard and technical as it gets. 1st year PHD course in Macro with 3 sequences ( I, II, III ). Though the material might be similar to other departments, the problem sets are notoriously difficult and technical. Level (High). Requirements (Everything :)- Optimal control, stochastic processes, linear algebra, differential equation, real analysis)
LSE Econometrics-Great material for introduction.
Econometrics Academy-Youtube channel dedicated to Econometrics
NYU Applied Econometrics-This is an intermediate level, Ph.D. course in Applied Econometrics.
NYU Applied Econometrics- Panel Data-Ph.D. course in Applied Econometrics for panel data.
Advise on how to survive first year PHD at a top institution
Notes Includes lecture notes on the main economics subject. Directed at graduate students
Textbooks The textbooks you will use during your first graduate studies