When we use "can" in questions, we change the position of the subject and the auxiliary verb and the main verb remains the same (as an infinitive without "to").
Where can I buy some gum?
Can she come to the office to get her things?
"Can" can also be used in the impersonal form when making a general statement that might not be about a specific person.
You can't steal things from people. (You're saying, in general, people can't steal things from other people.)
Modal verbs are a special class of auxiliary verb that is used to express conditions, necessity, obligation, ability, and wishful desire. Example: Shall, Should, Will, Would, May, Might, Can, Could, Must