This software is simply an interface for using youtube-dl (here) as a video feed downloader. You simply log yourself to youtube and the application will automatically download the latest videos from the channels you follow on youtube. The videos will be saved on your computer as a regular video file.
To work the application just need a youtube token. For that you simply need to launch the application and click on the big login button. Then login to your youtube account and copy and past the code that will be generated into the application (as the Auth code) and let it do it's work.
Youtube enable you to get real HD videos (1080p and more). But localtube (youtube-dl actually) need to download the video and audio separately and then merge them. In order to do the merging you need to install ffmpeg. Once installed localtube will automatically switch to downloading the best quality available.
sudo apt install ffmpeg