The present perfect shows continuity between a relationship or an action that began in the past and continues into the present. It is formed with the simple present of HAVE plus the past participle.
The present progressive, also called the present continuous, is formed with the verb BE conjugated in the simple present followed by a present participle.
The subject of a sentence refers to the person or thing that performs the action of a verb. A subject pronoun is often used to replace this person or thing in subsequent sentences to avoid repetition.