I'm going to assume that you are happy with your book. (As happy as a writer can be about their own work). That it's been edited a million times, spellchecked and meets the standard you want to put your name to. You've formatted it according to the Style Guide and now that it's practically perfect, you want to upload it to Smashwords.
Log in to Smashwords, click the Publish tab and a form will appear. The first section includes the Title, Synopsis, Language and Adult Content option. Pick a relevant yet catchy title. Clunky titles with no thought don't appeal. All of this information can be updated so don't panic if you think of a better name later. Select the correct language and tick the relevant option on adult content.
The Synopsis is a huge deal. Aside from the cover image and the title, the synopsis is the one that will entice readers. A well-written synopsis could encourage readers to download a sample of your book or better yet, buy a copy. The synopsis is also the part that can repulse a reader so work hard on this one. It should be relatively concise and intriguing - don't give too much information away but lead the reader to the best points in your story. Make them want to read more. This is the bit that fails the most when I am looking for a new book to read. There are quite a few poor efforts on Smashwords (like I can talk) that are doing a disservice to good writers who just don't have a clue what a synopsis should be. It has to be well written and engaging because it's technically a quick sample of your writing. If it's boring, readers will assume that the same goes for your whole book - be aware and be careful!
The next section is pricing and sampling. You have three options in pricing. Either make the book free, allow your readers to determine a price or set it at a price you are comfortable with. You have to set a price to be considered for the Premium Catalog, as far as I know. But you can generate coupons with 25%, 50% or even 100% off. These coupons have time limits and you can see which coupons, if any, each sale used.
Sampling is a difficult one. You don't have to enable it but I personally think it is worthwhile. I wouldn't risk spending money on an unknown writer if I hadn't read a sample of their work first. You can set it to a certain percentage and this is where a lot of writers differ in opinion. You have to give the reader a good taster of your work but when is it too much? If you have a novel, could a long sample give too much away? Or, could it be that the reader is so close to the end that they make a purchase because they are desperate to know what happens next? That's up to you to decide.
The next two sections are categories and tags. You can choose up to two different categories, including the sub-sections. If your book teeters on the edge of genres then you can include both. Handy. The tags are there to help people search for relevant material. Think about what you would search for if you were looking for a book like yours. The tags are very useful and probably undervalued by some people. There are a lot of books on Smashwords, give yours the best chance possible at being discovered.
The next section gives you the option of selecting various different formats to convert your book into. The more you choose, the more options your reader has. Choice is always a good thing. The more versions there are available of your book, the wider the potential audience could be.
The final sections are the cover image, the book file and the publishing agreement. The cover image is optional but you want to catch the eye of people searching for books. Manuscripts can be uploaded by word document or rich text file. If you update your manuscript at a later date, people who have already downloaded it will still have access to the old version. By clicking publish you are automatically agreeing to Smashword's publishing agreement. Clicking publish takes a few moments because of the time it takes for the file to convert. Providing you followed the style guide, there will be no need for further adjustments.
That's it. Your book is now online at Smashwords and available for sale.