When to use “need“
“Need” can either act as a modal verb or as a main verb. Because of this, it is called a semi-modal verb.
When “need” is used as a modal verb, it is followed by the base form of a main verb, and doesn’t have -s in the third person singular.
The modal verb “need” is almost always used in negative sentences and questions.
When “need” acts as the main verb:
It takes “s“ in the third person singular;
It is followed by an infinitive with “to“;
In the interrogative form, “do“ is used;
In the negative form, the auxiliary verb “don’t“ is used;