Hojekang, The two things that I know of that will cause your symptoms are a bad master cylinder or leaking brake fluid. Both of these are serious problems, because a little leak can turn into a big leak in a big hurry. If you are certain you have no leaks, and the pedal slowly goes to the floor when you are trying to maintain pressure, like at a stop sign or red light, then bleeding your brakes will NOT solve the problem. It is almost certainly the master cylinder that needs to be replaced.
Bench bleed instructions as well as a pair of plastic hoses and fittings should come with the new/rebuilt cylinder. You do not need special tools. Just keep everything nice and clean. If you are not confident that you can do the work, take it to a mechanic. Brakes are not something to take chances with.
You have been very lucky to go two years without a catastrophic failure. The owner'* manual for my old '49 Plymouth offered some sage advice regarding brakes. "If your car won't go, there you are...but if your car won't stop, where are you?"