i want to become a pilot, what shall i do?

Take flying lessons .

Do you want to be a Commercial Pilot, (i.e. fly for the airlines) or just get a pilots license to fly for pleasure.
A Private Pilots License will cost you around $8000.00.. To be able to instruct other people will require a Commercial / Instrument / Instructors Rating, which you can add around another $20,000. In addition to the pilot's license you will probably need to get a 4 year degree.
The other way is to get your 4 year degree and join the military and apply for pilots school.
The one thing to take into consideration is if your health starts to go bad and you cannot keep your medical certificate, then you cannot fly for hire, but you may still be able to fly for pleasure.

Well, you have a dream, that is the first step!
Next you have to figure out what you want to fly. Are you looking towards helicopters, airplanes, hot air balloons, gliders, space shuttle, drones, etc, etc. This is where you have to be honest with yourself, and also choose a path that fits you. If you are wearing glasses already, than the military is going to be a difficult path, which would also affect test pilot or NASA programs. Helicopters are kind of a small community, and a lot more expensive to fly, most go thru military, but you can go the civilian route as well.
Each one of those will have a slightly different way of getting there, but they all start with flying lessons and the drive and desire to be up there among the clouds. I strongly encourage you to find a school and take some lessons. take out a loan and negotiate with the flight school to get the best price, and fly, fly fly!
Good luck!