http://isboxer.com/wiki/WoW:FTL

The way it works is the 3 FTL functions (follow, assist, and target) are set up with in-game macros bound on different keys. The modifiers tell the in-game bindings which person to follow, assist, or target. The macro knows that if Shift+F11 for example) is passed, it should follow the character in slot 1. You do not need to do any special configuration to make it work. It just does.

The Quick Start Guide should help you with this and other beginner questions: http://isboxer.com/wiki/WoW:Quick_Start_Guide