1992 Chevy Cavalier leaking brakes without a trace

Brakes problem
1992 Chevy Cavalier 4 cyl Front Wheel Drive Automatic

hi... my brakes all of a sudden began getting squishy. upon inspection there is no visible sine of leaks. i can watch the fluid slowly drop as im filling it up while the car is running. the lvl dost seem to drop when the cars not running . it drops fast when brake is applied. i looked the system over well. as for how the brakes respond... it seems that only the front right tire grabs when im able to get any pressure. with the tires off, ic no compression on the f left roter.

I dont know whats wrong ... keep in mind i am a layman

any advice for repairs would be appreciated.