* The cat sat on the mat. (The subject is "the cat")
* Sarah loves to bake cookies. (The subject is "Sarah")
* The red car zoomed down the street. (The subject is "the red car")
* Running is a great way to exercise. (The subject is "running")
The subject is the part of the sentence that tells us who or what is doing or being something. It's usually a noun or pronoun.