The clone is pretty much identical to the Marushin. Exploded parts diagrams can be found here:
http://tech.airsoftcanada.com/Marushin
The stock attaches to the receiver with a large [usually hex] screw which goes into the back of the receiver, underneath the safety switch. If you have an M4 stock tube, depending on the model, the screw is either inside (like a TM stock tube attaches) or there'll be a hex screw on the base (if it's a "realistic style" tube, which screws on with a castle nut -- which means you have to remove the buffer tube first).