In both Pikmin games, bridges are shortcuts or paths to new areas. These bridges need to be built before they can be walked across, which is done by Pikmin. Before being built, bridges look like a tree stump or a log on its side, but when Pikmin hit them they will eventually start rolling out. When fully built, the "complete" tune will play and the Pikmin will go into Idle Status. The more Pikmin on the bridge, the faster it will be built.
After a few days of the bridge being built, Sheargrubs will start unbuilding it when a day starts. It is best to kill these quickly!
The first main glitch is a very common one, and involves the Sheargrubs. Firstly, get Purple Pikmin (Although it will work with any Pikmin) and take them to where the shergrubs are unbuilding the bridge in the Awakening Wood. Wait until is has been unbuilt a little bit and then pound purple Pikmin on them. Sometimes, Purple Pikmin will vanish! They are actually under the bridge, stuck there, not drowning. The only way to move them is to go into a Cave (They will return to the ships pod) or wait until Sunset (Which will kill them).