It's a bit of a faff but pretty simple - with a Schrader valve that is. Never tried it with a Presta.
What I do is just deflate the tyre with the wheel on the bike (upside down) and remove the core.
Halfords do valve core tools for a couple of quid.
With the valve at the bottom of the wheel, pop a small funnel or similar into the valve and pour the required amount into it. This is the faffy bit as the bottle apparently has to be shaken upside down and the liquid squirted immdediatly into the tube. Once it's in, cover the valve and rotate the wheel slowly to coat the inside of the tube.
Refit the core, inflate the tyre and tell the p*****re fairy to **** off.
A ten quid bottle will do 6-8 tubes.