Yes, when instructions say "install from aminet" that means download the thing. Then your startup-sequence might find it, assuming you unextracted the download and put FBlit program in your c drawer. And always assuming that you didn't replace the entire startup-sequence, but added the line to it.
http://aminet.netGo there, you will find FBlit.
You will also need WBCtrl, although you should have that in your Distribution drawer as per the instructions. You could try reading them, I don't just post links for my own entertainment.
EDIT: You didn't actually get back to me to tell you which Kickstart ROM you are trying to do this with. Consequently, it's very tricky for me to help you any further.