2001 Chevrolet Tracker brakes

Applying the brakes at high speeds is ok, it's when you stop then proceed at a slower pace that the pedal occasionally goes to the within an inch of the floor but still stops. A quick tap of the pedal and it's hard again. Brakes are only a year old and the fluid is ok. There appear to be no leaks, fluid or air. Again this does not happen every time you apply the brakes, even with the slower speeds. It's mothers car so I want to get it fixed as soon as possible, but since we are both in brokesville, I have to try and do it myself. If you can help that would be great, when I can get a donation to you all I will do it, man of my word..Thanx alot
Mike