Subject -verb agreement OR

https://dictionary.cambridge.org/grammar/british-grammar/need

When used as a main verb:

You need to study. You don't need to study. Do you need to study? Don't you need to study?

When used as a helping verb:

We need go there. We needn't go there. (Don't say, "We don't need....")

Note: Some people use "We need to go there" in affirmative; and "We need not go there" in negatives.