what's a difference between "need" and "need to"

Please help me. I've read a lot of definitions of usage of both words and I can't understand it :( Can you explain like to a child what's the difference?

("need" is used as a modal verb only in present tense questions and negations)


*Ruth needs to see the doctor today.
*Does Ruth need to see the doctor today?
*Need Ruth see the doctor today?
*Ruth doesn’t need to see the doctor today.
*Ruth needn’t see the doctor today.

*They didn’t need to return the books to the library today ( = it wasn’t necessary and we don’t know if they did or not)
*They needn’t have returned the books to the library today. ( = it wasn’t necessary but they did nonetheless.)

need to is a verb so you can say I need some money ;you use need to if in your tens are two verbs first need second eg.go so you say I need to go to school.to is between two verbs. It's my opinion and I'm not sure