Dear student,
A negative sentence uses not or do not
For eg: I do not know how to dance.
A positive sentence says what something is, has or does.
For eg: Birds can fly.
The cow gives milk.
A comparative sentence compares two objects.
For eg: Bananas are more nutritious than mangoes.
A superlative sentence is used when more then two objects are being compared.
For eg: She is the tallest girl in my class.
Jupiter is the largest planet in the solar system.
Regards