A driveshaft is responsible for transferring engine electric power from the transmitting to the differential and onto the drive wheels. A driveshaft could be one or two pieces with a centre support bearing in the middle. There are universal joints at either end of the driveshaft which act as flex joints that permit the differential to go upward when the car contacts a bump. A front driveshaft yoke can be used to connect to the tranny while a back driveshaft flange can be used to hook up to the differential. On older models the rear U joint bolts right to the differential without utilizing a rear flange. On entrance wheel drive cars there are two travel shafts which are known as CV axles.
Driveshaft themselves have hardly any problems with the exception of becoming bent if they are exposed to an obstruction. Alternatively the U joints could cause complications which are a part of the driveshaft such as chirping and clucking when the car is moving or put into gear.
Something you should know that might not exactly be thought of is whenever a driveshaft is removed the automobile will no longer be in park. The car will roll since the link between the drive wheels and tranny is removed. You need to raise the car or truck up using a ground jack and jackstays. Put on protective eyewear and gloves before starting.
Tag the driveshaft orientation before beginning. This will help go back the driveshaft to its primary location on the differential which can help avoid driveline vibrations after the driveshaft is reinstalled.
Using a plastic hammer delicately shock the driveshaft loose from the differential flange by striking the trunk yoke (U joint mount). At this point the back half of the shaft will end up being free so hang onto it. On some vehicles there will be a middle support which must be undone by taking out the two middle support installation bolts. When removing a mature vehicle drive shaft apply electrical tape to wrap around the u joint cups so they don’t fall off and relieve the glass needle bearings.

On front wheel travel cars the driveshaft is not used. The transmitting and differential is mixed into one unit called a transaxle.

All shafts are reassembled with fresh universal joints and CV centering kits with grease fittings and so are then completely greased with the correct lubricant. All shafts are straightened and computer balanced and Front Drive Shaft analyzed to closer tolerances than OEM technical specs.
The drive shaft is the part on the lower proper side of the picture. The other end of it might be connected to the transmission.