This page details how to use TubePress for Wix. It assumes that you already have a Wix website up and running; if not, Wix offers excellent documentation to get you started. TubePress is available to Wix.com as an "app" in the Wix App Market. As such, Wix provides detailed documentation on how to use the App Market.
For the sake of completeness, here's how to add TubePress to your site.
Inside the Wix Editor, click the App Market button.
The Wix App Market window will open. In the search box at the top left, type in tubepress and hit enter.
The TubePress app will show in your search results. Click the "Add to Site" button to add TubePress to your site.
TubePress will be added to your site in a "box" that you may now move around and resize to your liking, just like any other Wix element.