One of the first thing you will learn in aikido are the rolls. It is not the roll you learn at school at PE classes, because that implies rolling over your spine. The aikido roll is performed in such a manner as to protect yourself from injury. When you are doing it really well, there should be almost no noise of hitting the ground, just a smooth rolling.
Most of the beginners have trouble with this forward roll, and with rolling in general. You hit yourself here and there until you really get the feel of it. It really helps to watch how others do it. You can watch the other in the dojo or even on tutorials on YouTube can help you a lot. The picture above is one illustrating a frequent and also really dangerous error in forward rolling. As each and every one of us has some reflexes that established along the time, we react differently when falling. However, most of us would, like this kid in the picture, put the hand down, to feel more secure as we try to find our balance. This is however totally wrong and can lead to sever injuries of the wrist and what not.
When making a forward roll, concentrate on keeping the circular movement, like this guy:
You can see the whole series of pictures here and keep in mind you can always learn from the senpai in your dojo and ask for explanations from them in case you are not sure whether you are doing it correctly. Maybe at the beginning you will think you can never make it, but with perseverance and patience you will eventually get the feel of how it is done.