Have your .png files ready. Skins should be 64x64 pixels (for slim or classic arms). Capes are typically 64x32.
Problem: You see your skin, but your friend sees Steve.
Solution: Your friend must also install the exact same mod. This mod does not change how vanilla Minecraft clients see you. It’s a peer-to-peer cosmetic layer. For servers, install the mod on the server side (drop the .jar into the server’s mods folder) to force all players to see skins. File name- TL-Skin-and-Cape-Mod-Forge-1.20.1.jar
This is the important part.