Welcome, emank.
There are a lot of cars. <count noun>
There is a lot of milk. <non-count noun>
There are lots of cars. <count noun>
There is lots of milk. <non-count noun>
Lots of people . . .
A lot of people . . .
Lots of milk . . .
A lot of milk . . .
Note, "a lot of" and "lots of" express the same meaning and they also occur in the same positions. The difference is this, "lots of" is colloquial, and not accepted as Standard English. Psst. I'm not so sure about "a lot of". I believe "a great deal of" is the more preferred, at least in some circles.
All the best.