You can preview clothing in studio by inserting a Shirt or Pants object into a character, then once you select the ShirtTemplate or PantsTemplate property, you should see a button that allows you to upload the clothing.
Note: You must open a published game to see this menu.
If you don’t want to upload the template to the site, you could place your clothing templates into your studio textures folder and reference it with the rbxasset://textures/ link.
