i answer in english ^^
You'll find the documentation here : https://wiki.recalbox.com/de/home
Some parts may be not totally translated, so you may also use the english wiki.
Recalbox is free. I shoudn't be sold by any companies proposing retrogaming console that, i repeat, contains illegal stuff (roms, bios and so on).
You'll find in the wiki or in the forum all you need to update and play with recalbox 😉