In English, we have the past, present and future tenses. Perfect tenses are sometimes referred to the retrospective tense. This means we use perfect tenses to look back from a point in time.
To make a perfect tense, we use a form of the auxiliary verb 'have' and the past participle. For example, in the present perfect we could say "I HAVE EATEN breakfast". We are looking back from now into the past. We are not interested when I had breakfast, only that I had breakfast at some time before now. So we are looking back from now.
The perfect tense is interested in the action, not the time, so we don't say exactly when something happened. You can't use a perfect tense with an exact time reference. If you want to give the exact time, you would have to use the past simple, so in this example "I HAD breakfast at 9am".
In this series of video lessons, you will learn when we use perfect tenses and why with lots of clear examples in context. You will also learn the difference between the present perfect, the past perfect and the future perfect.