Can anyone tell me how exactly i can add another sub to my acoount,thing is i did it once but i cant figure out how i did it the first time.I looked at the lorebook but it didnt really help anyone know how to do this?
When I've done it before, it was when I had just purchased an expansion. This was clear back when Moria first came out, but I think the same process still works with the newer purchases that involve adding a purchase key to your account, like the Rohan pre-order, or Mithril Edition bundle, or Isengard (if bought through the web store rather than the in-game store). I don't know of any way that doesn't involve having just made such a purchase (though there may well be one).
When adding a purchase key, you first log into your existing account and put in the key, and then the website asks which of your subscriptions to apply that key to. Creating a new subscription to add the key to should be one of the available choices. By creating a new subscription this way while logged into your existing account, you can have that new subscription tied to the same account.
Keep in mind, the only advantage to having them on the same account is that they share the same login name and password, so you have one less set of login info to remember. Things like Turbine Points, which expansions are unlocked, etc., though they often get referred to as being "account-wide", are really subscription-wide. You can't, for instance, use points earned on one subscription to buy content for the other one just because they're under the same Turbine account.