There are several ways to install Minecraft mods like this. Here are the instructions for older versions of the mod (1.6 versions mainly):

This will bring up an installer from where you can chose which Minecraft Profile you want to mod, and what you want to call the new profile. Simply download the file, right-click it, and then select “Open with > Java Platform SE Binary”. Installing the XRay Mod has become extremely simple for newer versions. The XRay Mod works with vanilla Minecraft, Forge, and LiteLoader. This mod changes Minecraft’s *.class files, making it incompatible with some mods ( OptiFine will break some stuff).

R: Redstone Finder (bugged, dont use a switch when this is on).

However, no known systems can detect the mod itself, but servers can have plugins installed which detect if a person suddenly finds a bunch of diamonds (which indicates the person is cheating). Most servers do not allow abilities (cheats) like the XRay Mod, and you will simply get banned if you are found to use it. While it also works on multiplayer servers, it is not advised to use it. It is pretty easy to use, when it is installed, just press “X” and xray turns on. Unlike hacked clients, the xray mod does not need a hacked client to work – it’s a mod (like the name refers to). It was originally developed during the Minecraft beta 1.4, but have since been updated to latest Minecraft versions.

The XRay Mod (x-ray), gives the player an advantage over other players with an added ability to see special ore blocks like coal, iron, gold, diamonds etc.

Download xray minecraft 1.8