Drop the downloaded .zip into %appdata%/.minecraft/resourcepacks (Windows) or ~/Library/Application Support/minecraft/resourcepacks (macOS), then enable it in Options → Resource Packs.
Furthermore, this pack is strictly prohibited on most public multiplayer servers. Using XRay on a survival server is considered cheating and will result in bans. As such, the XRay 1.12.2 pack is best reserved for worlds, creative building projects where you need to clear out underground areas, or testing environments. x ray 1.12 2 resource pack
The result? You stand at the surface and look down to see exactly where the diamond ore is hiding 30 blocks below your feet. Drop the downloaded