Pages is a fantastic program, and the rep at Best Buy has absolutely no financial or other incentive to recommend it other than that he or she shares my opinion of it, presumably after having listened to what you want to accomplish. No knock on LibreOffice or other alternatives (including Microsoft Office) intended.
As stated above, you do already have access to the Mac App Store. Presuming that you already have an iTunes account, you would use those credentials to log into the Mac App Store (no need to create a new account unless you have never bought anything from iTunes and have no account there).
If you could give us some more information about your machine (model, RAM level, that sort of thing), we could advise on whether your best option would be to upgrade to Yosemite and get the latest version of Pages (very good) or if you should stay where you are for now and buy the older '09 version as Johnodd suggested.