First, You can equip them if you buy textures in the shop or in the market. There are certain textures for you to buy, for a certain bodypart of your tori.
Second, If you want to sell textures, you make a preview for them to sell, but you need to fill out some details. Like this:
Price of your texture:
Who made the texture:
What size or resolution is the texture in:
What kind of Payment to do you accept:
Will you recolor it:
Third, If you are able to sell your set to someone, it is you to decide whether to send it by PM or by email.
And etc. But around here, we call them heads or sets. Calling them 'texture' sounds pretty lame.
Also, if you are just a newbie, then Welcome To Toribash. Enjoy your stay. ;)