Both CreateSpace and Lulu allow you to upload regular Word documents (doc, docx, rtf) and also PDFs. The latter is generally more useful if your book contains a lot of images, tables, or special fonts, because they can be embedded and their location in the document is fixed and less likely to be messed up in a conversion. I have to admit, I've never done this so have no idea of the process. If your book is solely text, a Word document should work fine.
When you upload a Word document the site converts it into a PDF "print ready file". You can download and review it - which I really recommend, as it will allow you to pick up any errors that have crept through either making the document or the conversion. If you're not happy, tweak the original document and upload again. Once you're happy you can proceed to publication.
Both sites will walk you through the process: filling in the title and author details; pricing; uploading the cover or using the on-site designer; uploading your file. It's easy enough if you follow the steps.
One of the steps is choosing your distribution channels, which I'll look at next time.