Why don't we see clouds everywhere in the air all the time?

We see clouds at a particular height,and not everywhere near the ground.I am not really well versed in the concept of cloud,but I felt the clouds would be lighter by the way they look.So,they should have been at the bottom instead of being at the top.
I will be waiting to know the reason for clouds being only at the top and not anywhere else around us at the ground.