Brake lines and fittings on 1999 gmc sierra 1500?

i have a 1999 gmc sierra z71 and the front brake lines rusted out before so i got them replaced and now the back one is rusted out and i need to know what to do to put the new one in because it goes along the frame above the gas tank. i also need to know what fittings are on both ends. one is connected to a hose in the back for the axle and right under the cab in the frame it connects to a box that seems to split everything to all of the brakes. i dont know what that box is though. any answers would help. thanks