What is written in bold is the subject, what is written in italic is the predicate and what is underlined is the object.
Maria is playing with her dolls
He is repairing his laptop
Ann is driving her car
Arnold is jumping the fence
Dad is writing a letter.
The Subject in a sentence is the noun or the pronoun which performs and action, the action performed is the predicate in which we find the verb. The object is a noun or a pronoun which is acted upon by the subject.