how do i add custom accessorys onto a roblox character?

i dont know how to add a acustom accesory to a player model like shoes etc

As an example, shoes.

You could make it as a an accessory (hat) and weld it to the feet by using a plugin. I personally user moon animation suite as it has a welder. It is pretty self explanitory once you get the a welding plugin. In this case, in moon animation suite's weld edit, you select the Leg, and weld it to the foot.