Not 100% sure but in a day or so you will probably get an email from planetside, who will send you a license and a link to the download, as that is the normal way it works. Might be a little more time in between due to xfrog having to inform planetside of a purchase, then have planetside give you a key.
you can always download the free version meanwhile that is available online, but will be limited until you get the license file.