Hi Paola,

“sees” is the third person present so we’d use it for present simple affirmative statements for he/she/it subjects (with “it” covering any other noun, too). So essentially any third person positive statement in the present simple, and not when we have a question, negative or imperative. One way to test this is if we have any other verb before see, such as “to do” for questions, or modal verbs. Does this answer your question?

Phil