A technique used in a number of tutorials is start with a mesh, delete all the vertices and then start adding new vertices with control left mouse click.
It seems this never works on a mac. At least there are a lot of forum posts out there saying it doesn't work and asking for help. I haven't yet found one that results in useful answer.
The user preferences, 'input' tab, shows very clearly what keys are bound to actions and allows you to reassign them but mouse gestures don't seem to be exposed to configuration with the same clarity.
I'm working on a macbook air with a three-button wheel mouse plugged in. I've tried turning 'emulate three button mouse' on and off, I've tried working with the inbuilt trackpad instead, I've tried all the combinations of modifier keys and mouse gestures I can think of.
I have come close to using harsh language.
Does anyone know how to add a vertex to a mesh on osx?