What do you do with cowhides

Obtain Cowhide by either killing cows, buying on the Grand Exchange or any other method.

In free to play, take it to the Al-Kharid Tannery, nearby the bank. ...

Pay the tanner 1 coin if it's regular tanned leather you want, or 3 coins if it's hard tanned leather. ...

Start sewing the leather into items you wish to sell.