How to input a character into my game (already downloaded some from the asset store)

I downloaded some characters from the asset store because they looked really good. I have already made a prefab that is just the default one (the grey thing) before i downloaded these awesome characters. I’m just wondering how to do this.

If anyone can tell me how to do this step by step, please tell me, i really want my game to look good. So please if you know how to do this tell me how to do this.

The tutorials are in the “Support” section.

There are many grey things.