You must have the Forge mod loader installed on your PC.
The filename translates to the for Forge , version 1.21 . file name tlskinandcapemodforge121jar
Here is a comprehensive breakdown of what this file is, how to install it, and why it’s a popular choice for the Minecraft community. What is tlskinandcapemodforge121jar? You must have the Forge mod loader installed on your PC
It is specifically built to sit in your mods folder alongside other popular additions like Biomes O' Plenty or JourneyMap without causing crashes. How to Install the Mod Correctly how to install it