Calibre can be found here. Once installed, Open calibre and it will look like this to begin with:

Adding and Converting E-books
To begin start adding books by click the Add books button that is circled in the photo. Navigate to the directory where your E-book is stored and select it.
Available E-book formats that are supported are: CBZ, CBR, CBC, CHM, EPUB, FB2, HTML, LIT, LRF, MOBI, ODT, PDF, PRC**, PDB, PML, RB, RTF, TCR, TXT
Your Calibre should look something like this:

Clicking on the highlighted edit meta information button will bring up all the information on the e-book. If nothing is displayed, add the ISBN number in the ISBN field
and click the highlighted fetch Metadata from server. (Amazon is a great resource for looking up ISBN numbers) Once the metadata is obtained, one can click the Download
cover button to download the thumbnail cover image of the E-book. Also this will display what formats this E-book is available in.

Now that the Metadata is in order for the e-book, it's time to convert the e-book into the format you need. To do this highlight the e-book on the main page and click
Convert E-book.

This will bring up a box with many features to play around with, The one we are looking for is the output format in the top right hand corner. The formats available for
ourput are: EPUB, FB2, OEB, LIT, LRF, MOBI, PDB, PML, RB, PDF, TCR, TXT. Simply click the downward triangle and select which format you would like the E-book to be
converted to. Once that is done, hit the ok button and Calibre will begin the conversion of the E-book.
Adding E-books to devices:
In this section I will attempt to cover as many devices as I believe readers will be using such as the Kindle, ipod/iPhone/iPad, and android devices.
Kindle:
Calibre has a content server which allows your computer to display it's online catalog to E-readers. make sure your Kindle is connected using the WiFi network
in your house. To turn on the content server, click the preference button at the main screen, it has a hammer for the icon. Once this is pulled up, click content server
in the box to the left:

In this section the first thing to do is change the server port from 8080 to 80. This is because the Kindle is unable to connect on port 8080. Once this is done, simply
click the start server button. You may want to click the Test server button to make sure the server is up. This will bring up a page of showing all the available E-books
in Calibre.
To Access the Content server simply direct the kindle to http://192.168.1.2:80/ <---- where the 192.168.1.2 is your ip address for the machine Calibre is hosted on.

Apple products
The only experience I've had with E-readers on Apple Products in the Stanza E-reader. To add books to Stanza. Use the Content Server mentioned above. You however, can use
standard port 8080. Download the Stanza app. Pull up Stanza on the iphone/ipod and choose, choose 'Online Catalog', then the '+' button in bottom right
Then Add Stanza Catalog, and enter a name for the new catalog. The address will be http://192.168.1.2:8080/stanza.
Where once again the 192.168.1.2 is the IP of the machine that is running Calibre.
Now you should be able to download the books individually.
Android:
My personal favorite for E-readers on Android is the Aldiko app.(Aldiko requires the E-books be in the .epub extension) How to found under heading "Questions regarding import.
P.S
For finding your IP address in Windows, open Command Prompt under Start> Programs> Accessories> Command prompt.
Once Command Prompt is open type : ipconfig and hit enter. Your IP adress will be under the listing of IPv4 address.
Linux: Open a terminal and type ifconfig -a
Mac: open the terminal window, type ifconfig then hit return. Your Ip will be listed under inet.