x-ray resource packs don't work any more, however a modded client will probably still be able to xray. If you get suspicious someone is using an xray mod, go into spectator (so you can legit xray) and check out their mining patterns.
X-ray texture packs basically just have no texture for blocks that aren't deemed necessary for the miner to see. Anti-X-ray plugins make changes to the way the world appears to the player so that you can't see too far down if no textures are present.
Just click the 'Open Resource Pack' folder button to open up the resource pack folder. Now, all you need to do to install John Smith Legacy is drag-and-drop it into the resource packs folder that you have now opened. That's it! Just drag and dropJohn Smith Legacy into the resource pack folder, and you are done!