What Is the Difference Between IngramSpark and Kindle Direct Publishing?

After the manuscript is edited, the pages are designed, and the cover looks beautiful, the indie author is faced with a perplexing question: what is the difference between IngramSpark and Kindle Direct Publishing (KDP)? What will they do for me? All I want to do is sell the book on Amazon; is this how I do it? OK, and maybe Barnes & Noble, and…WalMart. And I want to buy copies of my book to sell at conferences; how do I do THAT? Oh, and can I get that in hard cover? And what about my eBook?