Definition: The material form or layout of a publication.
A good idea to do with your books is take time to make it formatted to what you are publishing it on. Ebooks look different than Paperbacks. Smashwords format is different than Kindle format. And so on. You can certainly go at this process on your own. Smashwords gives you a book to read about how to format correctly for them. You can order proofs to see how things will look before you push publish. I highly HIGHLY advise you ALWAYS look at your work before you hit publish. You never know what crazy things can happen during an upload or something.
You can also pay people to format your book for you. These people typically have done this before. But just to be safe I would ask how many they have done. Many times people won't advertise they will format your book without having experience doing so.