• A lot of and lots of mean the same.

EXAMPLE: I don't have a lot of money. / I don't have lots of money.

• A lot of and lots of can be used for singular uncountable nouns or plural countable nouns.

EXAMPLE: A lot of/lots of sand has got into my shoes. (Uncountable nouns)
EXAMPLE: I can eat a lot f/lots of grapes when I want to. (Countable nouns)

• When we use a lot of/lots of with a plural subject, we use a plural verb.

EXAMPLE: A lot of/lots of replies were received in response to her advertisement.

• When we use a lot of/lots of with a singular subject, we use a singular verb.

EXAMPLE: A lot of/lots of false information was given to the tax authorities.

• We use a lot of/lots of in positive statements.

EXAMPLE: We had a lot of/lots of fun at the funfair.