Sounds like you need to bleed 'em. Starting at the wheel farthest from the master stick a short piece of hose, preferably clear hose, on the bleeder nipple on the wheel cylinder and stick the other end of the hose in a small clear jar with enough brake fluid in it to cover the end of the hose. About 1/2 a jar is good. With the cover off the master and a full bottle of fluid at the ready, crack the bleeder open and have a helper press on the pedal. Watch the fluid coming out of the wheel cylinder for air bubbles. Have your helper hold the pedal down when it reaches the floor and alert you so you can close the bleeder. He may now release the pedal. Repeat until no more bubbles exit the wheel cylinder. Have your helper keep an eye on the fluid level in the master and top it up as needed. Now move to the next farthest wheel and repeat the process. Do not allow the master to go dry or you'll have to start all over.
Good luck and welcome to the forum!