Transfering digital books from my computer to my Ipad

I had an original Nook ebook reader and have replaced it with an Ipad mini.  I 've put Adobe digitial editions on my Ipad and now I have put it on my new PC computer  Since I do reviewing I download ebooks from NetGalley and Edelweiss onto my computer but I'm finding that I can't load them onto my Ipad.  When I connect the Ipad to the computer nothing shows up in Adobe Digitial and if I have the books on the computer they don't just automatically appear on the Ipad.  Does anyone know how to get the books from the computer to the IPad?  Or do I have to only use the Ipad to download the books?

Merle1104