In English, an infinitive is a verbal noun that typically follows the word "to" and functions as a subject, direct object, or predicate nominative. For example:

"To swim is my favorite activity." (In this sentence, "to swim" is the infinitive and functions as the subject of the sentence.)

"I want to swim every day." (In this sentence, "to swim" is the infinitive and functions as the direct object of the verb "want.")

"My goal is to swim in the Olympics." (In this sentence, "to swim" is the infinitive and functions as the predicate nominative of the verb "is.")

A noun is a word that refers to a person, place, thing, or idea. Nouns can function as the subject or object of a verb, or as the object of a preposition. For example:

"The cat chased the mouse." (In this sentence, "cat" and "mouse" are both nouns. "Cat" is the subject of the verb "chased," and "mouse" is the object.)

"I went to the store." (In this sentence, "store" is a noun. It is the object of the preposition "to.")

So, the main difference between infinitives and nouns is their function in a sentence. Infinitives typically follow the word "to" and can function as a subject, direct object, or predicate nominative, while nouns can function as the subject, object, or object of a preposition in a sentence.