Extra: Present perfect - 1

It is useful to distinguish two uses of the Present Perfect Tense.

Use 1 Unspecified Time Before Now
We use the Present Perfect to say that an action happened at an unspecified time before now.
The exact time is not important. 

Examples:

What is an unspecified time before?
The concept of "unspecified time" can be very confusing to English learners.
It is best to associate Present Perfect with the following topics: