Drum brakes leaking

[Sonicman]

I've been rebuilding my engine and some other stuff in the engine area the last 2 weeks. I get under the truck tonight to take off the manual steering box and notice alot of brake fluid running down the wheel and tire on the front drivers side. I have not had time to investigate yet. So......where do I start? I will check the brake bleeder just in case. But I don't know where to go from there. I've never messed with drum brakes before. Please help.