how do you add a note onto someone's Tumblr post?

[Christopher]

There are already people who have added notes, but I can't find what I need to do to be able to add a note onto the post as well. I would like to know this, but cannot find any button or other method by which I can add a note.

[Scaattie]

You reblog the post then write the comment in the white box at the bottom, before you click reblog the second time