It's not something that can be summed up in a few sentences.
However, as best I can... CreateSpace is a POD service for paperbacks, in association with Amazon. Free publishing with royalties paid dependent on book size, etc. Sales through CreateSpace or Amazon, with MUCH better royalties through CreateSpace though you have to point people to the page yourself - the Amazon listing is searchable and so on. Note that it's not a choice: if you publish through CreateSpace, your book appears on both sites.
KDP is Kindle Direct Publishing, also in association with Amazon. Again, free publishing with royalties. Electronic only, though you can publish the same book on both services and they both get listed together on Amazon.
ISBN is free with CreateSpace unless you want to buy your own (which gives you more freedom to move to another publisher if you want to, for example). No ISBN needed for Kindle unless you want to buy one.
CreateSpace is at https://www.createspace.com/ and KDP is at https://kdp.amazon.com/self-publishing/signin
As for book covers, you can design your own if you want to (my 'other' KDP title is "ReQuiEM" - Really Quick Easy Marketing - and I did that cover myself in a graphics program). I hired a pro for the main book cover, though, through Elance - costs vary wildly as with most freelancing: you can get someone for $50 or $300, depending on what you want. I picked someone whose portfolio made me stop and look.
Hopefully that'll help a bit even though it's very basic. Time for another hub or three, I guess, with more info. :)