it does sound like a master cylinder problem. Bad seals on the piston/plunger let hydraulic fluid leak past and the pedal will go to the floor. If that’s the case, you don’t necessarily end up with fluid on the ground or low on fluid. If you pump the brakes, does it build pressure? Pumping the breaks quickly allows you to build pressure faster than it leaks past the seals. Symptomatic of master cylinder problems.
Air in the lines would be fixed by bleeding the brakes, but air in the lines normally just makes the brakes spongy and doesn’t allow the brake pedal to go all the way to the floor, unless it is a lot of air. Normally the sign of a leaky brake line.
Brakes are kind of important. If you’re not comfortable diagnosing and fixing the problems, I would have a mechanic look at it.