Compile the file and MikTeX will automatically download everything it needs to compile the file if it is not there already (assuming you let MikTeX install what it needs on the fly - this is set. How do you get started? First, go here BEAMER CLASS EXAMPLES and download the first example, example-1.tex.
Use BEAMER and forget the other stuff, especially powerpoint. You will find that, as OS X is a UNIX-based environment, working with TeXnology may. Because the purpose of the Latex Compiler is to make preparing Latex documents as simple as possible, you can never go wrong with the Online Latex Compile, an easy to use solution for professionals as well as basic computer users.
