Brake Line Help Needed!!

I bought I Nov a Kitfox III. My first airplane and I am anxious to fly as a new Student Pilot. I noticed this weekend the left brake was spongy and had no fluid in it. I was told to add AV brake fluid by getting a pump oil can, add the fluid and a "fuel line type tube" and to pump it up thru the brake assembly down by the wheel. Nothing seems to be getting into the lines and hydaulic brake up on the pedal. Can someone give me some advise?

I just flushed my brakes tonight.

In order to get the fluid to flow from the bleeder valve to the master cylinder, you need to open the "fill hole" on the top of the MC. Mine had a socket head cap screw (allen socket screw) that threaded into this port.