Pipe placement is important. If you want to remove items from a furnace, for example, then a wooden pipe needs to be attached to the side of the furnace. A pipe connected to the top of a furnace places items into the top spot, and a pipe connected to the bottom of a furnace puts items into the bottom spot.
The crafting recipes
Wooden pipes are for extracting items from any container (e.g. furnace, chest and other things that may hold items). It must be powered by an adjacent engine to function.
Cobblestone pipes carry items along the pipe network. They will not connect to stone pipes.
Stone pipes carry items along the pipe network. They will not connect to cobblestone pipes.
Iron pipes have only one output. It can be changed with redstone or a wrench. They can't output into a wooden pipe.
Gold pipes can boost the speed of items passing through them when supplied with a redstone current
Diamond pipes can filter items to different output pipes based on a user-defined filter.
Obsidian pipes will pick up items off the ground. Their collection range will increase when powered by an engine.
Stripe pipe will place or pick up an object that is in front of it when powered by an engine.
Main article: Waterproof Pipes
Waterproof pipes can carry buildcraft compatible liquids around. They require pipe waterproof in their construction.
Main article: Conductive Pipes