I'm a techie, and I had to dig for a while to find the answers.
http://manual.calibre-ebook.com/faq.html has most of the steps. I've cut and pasted them here for convenience.
On your Calibre server/laptop/desktop computer:
The easiest way to browse your calibre collection on your Apple device (iPad/iPhone/iPod) is by using the calibre content server, which makes your collection available over the net. First perform the following steps in calibre
Set the Preferred Output Format in calibre to EPUB (The output format can be set under Preferences->Interface->Behavior)
Set the output profile to iPad (this will work for iPhone/iPods as well), under Preferences->Conversion->Common Options->Page Setup
Convert the books you want to read on your iPhone to EPUB format by selecting them and clicking the Convert button.
Turn on the Content Server in calibre‘s preferences and leave calibre running.
Now on your iPad/iPhone you have two choices, use either iBooks (version 1.2 and later) or Stanza (version 3.0 and later). Both are available free from the app store.
This part isn't in the FAQ:
If you're on a Mac, you'll need to figure out your IP address. To do that, click on the apple in the upper left corner of your screen, then "System Preferences" then "Network" which is under "Internet and Wireless". In the left column, click on the network connection option you use. In the righthand box, it will say "Status: Connected" And something similar to, "
Wi-Fi is connected to
network and has the IP address
192.168.1.2"
On your iPad:
Start the Safari browser and type in the IP address and port of the computer running the calibre server, like this:
http://192.168.1.2:8080/
Replace 192.168.1.2 with the local IP address of the computer running calibre [the address found in system preferences/network]. If you have changed the port the calibre content server is running on, you will have to change 8080 as well to the new port. The local IP address is the IP address you computer is assigned on your home network. A quick Google search will tell you how to find out your local IP address.
You will see a list of books in Safari, just click on the epub link for whichever book you want to read, Safari will then prompt you to open it with iBooks.
I clicked on "Open in ..." and it let me choose one of the several eReaders that I'm test driving on my iPad.
Hope this helps!