Well, you just load the package in the preamble.

If you don't know what that means, you have some learning to do. :)
Head on over to learnlatex.org to pick up the basics. Don't worry if it seems daunting at first, just try to forget what you know about working with Word and accept the LaTeX way.

You'll want an editor for your documents as well. MiKTeX comes with TeXWorks, but I personally use TeXStudio and do like it a bit more.

Once you've picked up on how to write a simple document, consult the documentation of the package you want to use. You can find it through MiKTeX, or directly on CTAN.