Use the present perfect to talk about recent events or a past event which the speaker feels s is connected with
the present. Use the past simple to talk about a finished action.
Certain n time expressions may be used with the past simple.
Basically, a sentence is a combination of two grammatical units—the subject and the predicate.
Subject
The subject of a sentence refers to what the sentence is about, often the
person or thing that carries out the action of the verb. The subject usually gives
a clear idea of what the sentence is about.
The subject can be a noun—either a common noun or a proper noun or a
verbal noun; a noun phrase; a pronoun; a subordinate clause; an infinitive.
In the following sentences, the underlined words form the subject of the sentence
and the subjects are nouns.