There are plenty of nice explainer videos on Youtube that show you how to use Gedmatch. These videos also explain what Admixture model to use so you can comprehend your DNA test results. I plan to write an in-depth article on the various admixture models (such as MDLP, Dodecad, Harappa etc.) used by Gedmatch. So you might want to check in a couple of weeks for more info on the models. In the meantime, I recommend the following two videos for an in-depth explanation of how to use the Gedmatch tool and interpret results from it.