Brake pedal goes to the floor

The first thing is to check for an external leak. Look in the brake fluid reservoir to see what the level is in the two chambers. If you need to add fluid, do not fill it. Also, be absolutely certain to not introduce any contamination from petroleum-based products like power steering fluid, engine oil, or transmission fluid. Doing that will cost more in repairs than the car is worth.

If there is still fluid in the reservoir, you may simply have a bad master cylinder. The clue is the fluid level will not be going down.

Look inside each tire for signs of wetness, and along the left side of the car. If you see a puddle forming there, the leak must be fixed, then the line must have the air bled out.