how do i import ebooks from calibre

I am long time user of PC, Kindle, Calibre and have built up a considerable library of epub ebooks. I have managed to connect the iPad to the PC via USB and have Calibre recognize iTunes, and send an ebook (epub) format from Calibre to iTunes or iPad (Ido not understand the relationship) and it went somewhere. Where did it go? I assume it is on the iPad somewhere. And once I find it, how do I read it? I did install iBooks -- but there does not seem to be any way of putting a book in its library. Same for Adobe Reader. I installed the app, but have no way of sending a PDF file from the PC to the iPad. Probably simple if I had some understanding of the file structure of the iPad -- is there an app for file browsing the iPad?