Need advice on what is the the best way to gain abdominal muscles quickly?

There isnt: No quick way: to gain the "six pack" that you are probably interested in involves not only building up the abdominal musculature but also burning off the overlying fat layer. This thus means overall fitness and so you not only need to do work outs directed at the abs (try the p90x ab ripper- can find this online), but also watch your diet, do cardio to burn fat etc.