I have a Minecraft Cape here.
Where does the cpae file have to be inserted so that the cpae in the game hangs on me?
This is not possible in a normal game. You only get capes through Optifine (nfn), other client extensions / mods, or you get one from Mojang that you can't change.
Capes can only be added through the Optifine and Labymod (and other) websites. Capes in Minecraft directly only work via banners and texture packs or mods.
You can only add capes through Optifine or something