Pool Algaecide, Clarifier & Floc

How to clear a green algae infested pool (in brief);
Make sure your pH is around 7.2 - 7.6 (the lower end is better).
Vacuum out larger patches where possible.
Brush pool then keep shocking with Shock Chlorine (or non-chlorine shock if you use bromine).
If your infestation is bad, use Algae Eliminator.
Once the water is white and cloudy the algae is dead. Get rid of the cloudiness with a Floc (heavy duty) or clarifier (for slight cloudiness).

Stop it coming back by regularly using Algicide, and keeping your pH and Sanitisers levels within range.