I'd like to be able to simply type herb and then press tab and have fish-shell tab-complete it to herbstclient. I've tried looking it up, but every result I can find has to do with overiding fish's autocomplete with tab rather than ctrl + f.
Do I need to create a fish script for this? If so, what should it look like and where should I put it?
Assuming that is a command you want an abbreviation: abbr herb herbstclient. Although you don't use [tab] to complete an abbreviation; you have to press [space] or [enter]. Note that the expansion can consist of multiple tokens. For example, this is one of my most often used abbreviations: abbr -a -g -- gcm 'git checkout master'. Also, abbreviations only get expanded in the command position; i.e., start of line or after a pipe, |, or semicolon. If you want that expansion elsewhere in a command line there are ways to achieve that but it's a bit more complicated.