I just squirt it on and then sort of rub it into the hair. A spray bottle would work much better though and not waste as much. I then use a wide comb and starting at the bottom work my way up combing it through. Then just let it dry.
If you don't have a wide comb you could just use your hands/fingers.
Don't use a brush, it tears the hair too much.
ETA- This is how I do it after a bath when the tail is wet. I've never put it on dry.
"Until one has loved an animal, part of one's soul remains unawakened..."
- Anatole France