This is actually the perfect thing for you to learn about your truck and gain some skills!!
Brakes on these old trucks are a pretty simple system. The only kind of hard thing to do is to work on the drums. But that is another lesson for another day.
You need to put on some old jeans, and a crummy sweatshirt, and go crawl around under the truck. Check the backside of each brake drum. There will be a line about the size of a #2 pencil running into the brake drum. Where this attatches is the 'wheel cylinder' this is probably leaking. With a leak that bad i would expect to see a lot of fresh fluid on one of them.
It is also possible that one of the lines is broken and needs to be worked on. Just start tracing brake lines from the master cylinder.
Once you find and fix the leak you will need to refill and bleed your brake system. Let me know when you are to that point and I will post more.
Crap...here comes my boss

Kyle