For MG and YA Novelists
You should include a one page maximum synopsis of the book. When you do this, include the character arc and ending.
For PB Authors
You should include the entire manuscript as an attachment (if by email) or printed out (if by post).
The manuscript should be double spaced. Also it should meet the publishing house’s length guidelines. If all the sites I find say 500 to 1000 words, how will I know that Simon & Schuster wants 400 words in their picture books? Thankfully you do know this, because I went to Austin’s SCBWI conference.
These are the standard differences. HOWEVER, before you send anything to any publishing house or agency, editor or agent, make sure you check their submission guidelines and follow them.