Hi, PortofPV, welcome to the forum! Good to "see" you and I hope you enjoy your visit(s).
You could put your Calibre library on the iPad - the problem would be that you'd always have to keep updating it. So, here's what I do:
I got a Dropbox account (it's an online cloud storage that's free for the first 2GB of storage). I put my Calibre library in the public folder part of Dropbox. As in, Calibre itself links and stores my books up "in the cloud." I do keep a local backup on my hard drive, but the one on Dropbox is Calibre's source.
Then, with it being in the Public folder of Dropbox, you can create a link to it so that you can access your library through any web browser (including Safari) and thus download books to your iPad. You browse to the book, press it and select the "Open In..." process for the app with which you want to read the ebook. You also can access your library through the free Dropbox app and download it that way.
But wait, there's more!
You'll want to research this, because I don't do it this way, but there is a way to have Calibre act as a server and, as long as your computer is on, you can browse through Calibre as if you are sitting at your home computer; you can look at tags, genres, etc.
Sometimes, I don't want to leave my computer on, so that's why I put my books in the cloud. I then use a (free, I think) program called Calibre2OPDS, which creates a browsable catalog in you Calibre folder in Dropbox. Once you create the catalog, which has an HTML extension, you can make a link and again access it via any web browser. I made a home screen bookmark with Safari so that all I have to do to access my library is press the icon and hey, presto! I'm at my catalog, browsing for a book.
So, while you can put your books physically on the iPad by dragging them through iTunes, I thought you might like to see other alternatives. Hope some of this is useful.
Oh, and you can set up Calibre so that you can send books to the iPad directly from Calibre, bypassing iTunes. I don't use that method either, but that's and option.
Anyway, good luck and happy reading!
Marilyn