I'm pretty new to this, so hopefully someone will chime in with more detailed information soon, and please correct me if I'm wrong on any of the following.
Importing Word into InDesign is not a problem (File: Place).
Basically what you need to start an ebook is a good, clean HTML file. Then some other files get attached to that. InDesign makes cleaner HTML than Word does, and it makes the other necessary files (which I don't think Word can do).
The most important thing about ebook formatting is that it has to be very linear, so the fancier layouts that you can create in InDesign won't translate to an ebook. (There are ways you can _make_ a fancy layout translate, at least in theory, but start with a simple project or you'll tear your hair out.) InDesign, when exporting to epub, will "read" the page from left to right and top to bottom and put things in that order.
Make sure everything you do in InDesign is done in paragraph and character styles -- no manual formatting.
When you're done setting up your document, go File: Export and under format choose EPUB. That will give you a document that should be readable in an epub-reading e-reader (~anything but Kindle). It will probably have some glitches and need some tweaking. That's where I bow out and hope some more experienced users chime in.
Two excellent free software programs are Sigil (for detailed editing of epub files) and Calibre (for changing from one e-book format to another and doing minor adjustments). Calibre can also work with an HTML file or a PDF, I think, so you may not need to work through InDesign. It depends on your workflow and the type of document.
Hi - eBook is a generic name (for a number of formats, from PDF to DPS). Assuming you mean ePub, (the format for ebook readers such as the Sony eReader and, with a plugin for InDesign, for the Kindle. Creating (and understanding) how ePubs work is not intuitive. InDesign CS5.5 is much better at creating ePubs than earlier versions. I suggest you get some training – from online sources such as Lynda.com e.g. http://www.lynda.com/InDesign-CS5-5-tutorials/to-EPUB-Kindle-and-iPad/82258-2.html, or Video2Brain: e.g. http://www.video2brain.com/en/products-92.htm
and there are some excellent books: One of the best is: Elizabeth Castro's "EPub, straight to the point"
if you can afford it, personal training is one of the best ways, in the UK for example, Certitec: http://www.certitec.com/adobe-training/indesign/indesign-1-day-epub.
Her geekness (Anne-Marie Concepcion) does not recommend Sigil for checking and editing ePubs – she recommends oXygen Author: http://www.oxygenxml.com/