the iBooks say its meant for iPad and iPhone, so I don't know what I can use to read books on my computer.
Normally you can't, that's why it says on every purchase page in the iBookstore that iOS device is required.
To read ebooks on your computer, you need to buy them from another source and use their free ereader, like Kindle, Nook, Kobo, or Googlebooks.
Mac App Store - Kindle
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