Add it before / after filling the fuel tank (FULL). Just pour complete bottle in it. It is recommended to use every oil change (about 5000 ~ 6000 kms).
I changed engine oil to Shell Helix Ultra 5w-30 & this cleaner, and for the first time, I saw a difference between D & S gear on Lahore ~ Multan highway. The sudden burst of power on S was amazing 150 is easy peasy now, while it was hard on motorway before. Last oil was Havoline Formula.
RON means Octane rating of the fuel, we have pathetic fuels, so it'll try to fix things that are caused by these low grade fuels.