PG has an essay that covers a lot of how this works (2005):

http://paulgraham.com/startupfunding.html

This Techcrunch article is about convertible notes but covers some of this stuff and has some good links in it (2012):

http://techcrunch.com/2012/04/07/convertible-note-seed-finan...

And a more lawyerly perspective (2010):

http://www.saul.com/media/tool/997_PDF_2534.pdf