i am new and i just want to know if there is a document where I can see how i buy and sell digital currencies (not bitcoins).
do you know some common providers?
In Bisq (former Bitsquare), for now, you always either sell or buy bitcoin, but it is your choice what the other currency will be. It can either be fiat or crypto, but either way you are using BTC. You can look at this video to get the idea on how to buy or sell cryptocurrency on Bisq https://www.youtube.com/watch?v=reQ0M1_SPsA