What to do if i had an asthma attck, my doctor prescribed me a combination medication, seretide, is it necessary?

Probably: Seretide is a "controller" inhaler. That means your condition- at this time- requires continual therapy to reduce he number of attacks you experience. The trick to controllers is that they must be used routinely as prescribed by your physician. They are not "rescue" inhalers like your albuterol which is to be used only when you have an attack. Good Luck