Using this app is as simple as accessing the video of interest through the 'browser' that comes integrated within the app itself. From there, simply press the green arrow located at the bottom of the screen.
At that moment you can choose what quality you want to download your video in, normally having many different resolution options adapted to the various terminals Android compatible with this app. Depending on the download format you choose, you might need an extra app to play your files.
The downloaded videos by default are sent your storage card, but you can easily move them at your whim if you'd prefer to store them in separate places. TubeMate YouTube Downloader is a very easy to use video downloader tool whose main trick is precisely that: you can download any video in seconds.