curing it is basically letting the die off finish dying off and then start to regrow, you can do this in a seperate container, or if your tank has no fish in it, you can do it in your main tank, this would also cycle the tank at the same time, because the die off will create an ammmonia spike, which would kick start your cycle, and or kill any fish or inverts you have
if you by locally and well cured lr then you can add some small amounts to the tank without any problems, but if you buy uncured or mail ordered then i would cure ti before putting it into an existing tank
if you have to cure it, all you do is put it into a container of salt water with a heater and powerhead, and let it go, doing water changes, until your ammonia and nitrites are zero and stay there
HTH and good luck