This question is focused on two wheel recumbent bicycles. The answer to the question, are they easy to ride, is yes and no. Everyone learned to balance while riding an upright bicycle at one time in their life, and learning to balance when riding a recumbent will be no different.
The basic difference between the two is the balance point. On an upright bicycle your legs hang down like a pendulum which can help provide a centering effect to help keep you upright, and your upper body is not constrained by a seat back so it can lean to one side or the other. On a recumbent your legs stick out in front of you so there is no pendulum effect, and your upper body is constrained by the seat back. Because of the balance difference recumbent bicycles need more speed to stay upright.
Ever watch a child just learning to ride? They wobble and they weave and they start and stop. It will be no different with a recumbent; you will look like a drunken sailor going down the street. But it will get better with practice. At some point riding a recumbent becomes second nature, and you will give it no thought.
Starting and stopping on a recumbent are definitely different. Your feet are up in the air instead of hanging down low to the ground. When coming to a stop you better be prepared to get one foot down because if you start to fall over you will go . . . all . . . the . . . way. There will be no stopping it. Starting up is different also. When pushing off you will have to get the second foot up on the pedal quickly to keep the speed up; with a recumbent you have less time to get the speed up. Again, it will become second nature; give it time.