Many people show their feelings with presents? What is the simple subject of the sentence? Presents?

No. Find the verb first. What is the action in this sentence?

Then ask yourself who or what is DOING that action.

People

Right.

Many people show their feelings with presents the answer is many people

Yes, the simple subject of the sentence "Many people show their feelings with presents" is "people". The simple subject is the main noun or pronoun that the sentence is about, and it is usually the subject of the main verb. In this sentence, "people" is the main subject that the sentence is talking about. The phrase "with presents" is a prepositional phrase that provides additional information about how people show their feelings.