First of all there are lots of myths about what causes it, as if it's an unnatural thing to happen. Secondly many people think that the plane isn't strong enough to withstand it and finally they think it's harder to fly a plane in turbulence than at any other time. By adding these things together most people, not unreasonably, think that turbulence is dangerous. The reality however is that as long as you have your seat belt securely fastened you're safe from injury, even though it may feel very uncomfortable.
In my experience the turbulence that has grabbed and shaken the imagination of the public is Clear Air Turbulence it's as if it has more sinister properties than any other form of turbulence. To a pilot this is just a description of where the turbulence may occur that is to say without the presence of the cloud that is normally associated with turbulence.
Turbulence is caused by air movements, and just because air can't be seen does that make what it does any moe dangerous? Of course not. Should be more concerned about turbulence in cloud? Of course not. In fact we needn't be concerned about either.
There are always large movement of air across the surface of the earth. The main reason is that when air gets warmed up it rises so air is drawn in from somewhere else to fill the space it leaves. If the air is drawn in from hundreds of miles away we feel the effect as wind. At the equator the ground gets heated up and when it rises air is drawn from the Polar Regions to replace it. So very roughly the wind comes from the poles towards the equator. Also very broadly speaking the air heats up over places like Africa, Europe or America and when that air rises, it is replaced by cooler air from over the sea areas. So there are winds going up and down the earth (North South) and another going across it (West East). When theses air masses collide the result is turbulence.
And if that's the big picture, the little picture is that it's happening all over the world in smaller ways, over towns and villages and over fields and deserts all combining to make the air full of bumps. A lot of air masses bumping into each other most days and places. But not all the time because there are days when you can fly for hours and hours without any turbulence.
If we could see the air it would look the currents of two rivers colliding and making the air choppy just like the water. As with many things in flying, seeing is believing and because we can't see the air we find it hard to believe that it behaves exactly like water. From the designers point of view there is enough data to know what forces an aircraft will fly through and so it's designed to be able to withstand them and with an extra margin as well.
However for additional safety we don't fly through storms where there is strong turbulence in fact all aircraft fly at least 20 miles from the centre of a storm because that's what international air law requires. All the pilots have to do in turbulence is turn on the seat belt signs and reduce speed by about 20 miles per hour. The main reason the seat belt signs are turned on, is to avoid costly litigation that might be the result of someone being 'hurt' during turbulence. Usually the cabin crew continue working so it can't be too much of a problem, so don't be misled by the seat belt signs!
Turbulence doesn't affect the handling of the aircraft it's just like driving a car over a bumpy road compared with a smooth road...one or two more corrections but nothing you'd be particularly aware of. It's no harder to fly a plane in turbulence than at any other time. Turbulence may be uncomfortable but that's not the same as dangerous.