Present perfect simple vs Past simple.

Hi, class!
In this video-lesson you'll learn the differences in use (usage) between the present perfect simple tense and the past simple tense.
If you're already familiar with the form of them you can skip until minute 2,05.
To review the lesson, you can follow these steps:

1. Watch the full video (or skip to the usage part)
2. When you feel you don't understand a concept. Rewind the video and play it again up to the point you didn't understood.
3. Take notes and make a diagram in a time-line with examples of present perfect and past simple.
4. Write questions about difficult aspects. We'll discuss on them in class.