The drawbridge is a block added by Tinker's Construct. It's used by many as a partial replacement for RedPower Frames for doorways and pathways. Not to let the name confuse you, this can send blocks in any direction, depending on the orientation you place it in. It has much less lag than Frames, and it hides it completely, so you don't have to create a pocket for it. The major downside is merely that all the blocks in a row must be the same type. This is solved by using the drawbridge to craft the Advanced Drawbridge.
The draw bridge's GUI is simple: in the far left slot, you put one block of what you want the drawbridge to look like, and in the far right slot you put the block you wish to output, 1 block to set and another to output. ( i.e. You want 2 blocks to be dispensed you need to put 3 blocks in the far right and apply a redstone signal.) In Mechworks 0.1.2, there are an additional five buttons: four large arrows pointing in the cardinal directions and a tiny square in the middle. The use of this is currently unknown.
The drawbridge works by redstone signal. It will place blocks out one at a time, starting from right next to the drawbridge block and going out from there. If the signal is cut off, it will pull blocks back in one at a time. Multiple drawbridges can work side-by-side. If you place a lever on the drawbridge, as levers do, it will not only send a signal to the block, but make the block a power source. So you can make three drawbridges work at once if you place a lever on the middle one. Alternatively, you can place redstone beside them (on top of them if you're not sending the blocks upwards) .
The drawbridge will never pick up any blocks it didn't place. You can destroy blocks anywhere on the drawbridge and it will pull in the ones after the break.