I have come across need to do something and need do something. My question is what's the difference between each other? My grammar book doesn't mention it
I think you should use "to do".
'do' is an auxillary, action verb: "you need to do [the thing]".
I have never hear a native english speaker use the: "I need do something." form.
Auxiliary verbs add functional or grammatical meaning to the clauses in which they appear. They perform their functions in several different ways:
- By expressing tense ( providing a time reference, i.e. past, present, or future)
- Grammatical aspect (expresses how verb relates to the flow of time)
- Modality (quantifies verbs) Voice (describes the relationship between the action expressed by the verb and the participants identified by the verb’s subject, object, etc.)
- Adds emphasis to a sentence
Auxiliary verbs almost always appear together with a main verb, and though there are only a few of them (do, be, and have are the main ones), they are among the most frequently occurring verbs in the English language.