Not hard, its just take practice, practice, and more work out on a rowing machine.
Length of the race is all depend on what regattas that you are on.
Single & double are the hardest to control, while quad & octuple sculls are a little easier. The rowing distances is relatively short, at 500~2000 meters & <12 minutes.
Rowing is the best exercise that your can get. It is a great cardiovascular exercise and uses every muscle in you body. It will take a little time to get your rhythm right, but once you get it, not thing physically feel better after your team mate fish you out of the water after you won a 2000 meters regatta.