I don’t think I was ever taught the “unit form” of something, but it basically just applies as follows:
111 = 1 Hundred, 1 Ten, 1 One.
725 = 7 Hundreds, 2 Tens, 5 Ones.
etc.

So, $2 in Unit form would either be:
2 Ones.
or
2 Dollars.

Hopefully that helps, have a great rest of your day! ^ ^
{-Ghostgate-}