Another acronym for the 2-4-1 deals I suspect.
Buying a rail ticket at Waterloo to Hamoton Court gives you a ticket that's valid for the 2-4-1 deal. Unless there are other places you intend to visit under 2-4-1, you don't have to buy a weekly travelcard.
Remember, if you do go for a weekly travelcard, you'll need to bring passport size photos.