For argument's sake, let's say your printer of choice sells you copies at $5.00. You can order as many books as you like for that cost (and you may get discounts for buying in bulk). You can take these books to a convention, or whatever, and hand sell them for whatever you like, and keep all the profit.
Let's say you decide to sell your book online for $10.00. Your printer will keep $5.00 of that and pay you the rest when you meet their payment threshold. This will vary by site, so it's worth checking out as if they have a high threshold it may be a while before you seen the money - if at all. However, if you take advantage of their distribution channels you may see even less of that $10 - because each of the distributors will want their own cut. For each copy of Conversations with Dragons I sell through Lulu I make $4.99. If I choose to use them to sell it through other retailers this drops to $0.40. This includes Amazon, so if you want to sell through Amazon I'd honestly recommend going through Createspace.
I use both Lulu and Createspace. The reason for this is it costs me a lot less in time and money to get copies from Lulu if I want to buy a proof, or copies to hand sell. However I've never sold a copy to a third party online through Lulu, and I have through Createspace/Amazon, so it's worth it for me to take the effort to do both. If you only plan to hand sell, or sell online, you might find it works better for you to just pick one.
Next time, uploading your file.