The file you will receive is a .png that contains the settings needed to create the brushes yourself in SAI (SAI does not have individual brush files).
To use, right-click an empty brush cell in SAI, choose a tool (pencil and bloopy are both Pencils, softy is a Watercolor) and adjust the settings to match the ones in the .png. There are no extra files for you to download or put into any folders-- all you have to do is copy the settings.
You can use these brushes for whatever you want, including stuff you intend to sell, as long as you aren't directly re-selling the brushes. You don't have to credit me when you use them.
Disclaimer: Because different tablet models have different sensitivities, your strokes may come out a little different. I use a Wacom Intuos 4, which has 2048 levels of pressure sensitivity.
COMPATIBLE WITH PAINT TOOL SAI ONLY.