Step 1: Look around the Wikiwijs to get to know how it works.
Step 2: Click on the button that says 'The perfect tense'
Step 3: Read the instructions of the perfect tense carefully and complete the check quiz.
Step 4: If you find the written instructions still a bit difficult, you can find a video when you click on 'extra', in which the perfect tense is explained as well. You can watch that if you have earphones.