It's very easy. Copy the URL, paste it in the text box, click the 'download' button and wait for a few seconds.
Configuration options are very reduced, in fact you can only choose the output folder and if you want the program to monitor youtube links and download them automatically.
The output format depeneds on the format it is in the website. If it's an old video it will be FLV, although if it's a new HD video, it will be MP4.
YouChoob is an useful prgram for all those users who want to save videos from Youtube in the HD to view them offline.