Any Dimension Mod 1.12.2 (2... - Mods - Minecraft - CurseForge
Search, download and run the Forge Installer (make sure you use the recommended version). Open your "mods" folder in your minecraft directory. If there isn't one, make one now. Download this mod, extract the JAR file into that "mods" folder. Open the Minecraft Client and select the Forge Profile. Run Minecraft Forge.