I did it myself | means | I, and only I, did it |
He (or John) did it himself | means | He (or John), and only he (or John), did it |
She (or Jane) did it herself | means | She (or Jane), and only she (or Jane), did it |
You did it yourself | means | You, and only you alone, did it |
You did it yourself | means | You, and only you alone, did it |
You did it yourselves | means | You and at least one other person, and only you and that other person (or those other people), did it |
We did it ourselves | means | I and at least one other person, and only I and that other person (or those other people), did it |
They did it themselves | means | Two or more people, and only those two or more people, did it |
I gave the book → John = I gave the book to John.
I gave John 2 books = I gave John two books.
I gave John more books than he wants = I gave John too many books.
I also gave a book to Mary = I gave a book to Mary, too.