CS:GO misc/keys are needed for opening cases with weapon finishes, if you want to get Free CS:GO Skins you must take part in Dmarket Giveaways. Every misc/key is suitable for a certain csgo case with the same name.
CS:GO Keys for Sale
A CS:GO misc/key can’t be obtained from the game process, but you can buy such items on DMarket. Buy skins for cheap now!