These two concepts of time and tense are not always kept apart, although they should be. Keeping them apart avoids confusions.
The first concept, time, is very common for everybody and is well understood despite the language. It is not a grammatical structure.
The second concept, tense, is a very important linguistic tool expressing time relations. Tenses, in most cases, correspond to time. However, there is a big variation between languages. In English, tenses don’t always correspond to time because they show us not only when the action takes place but also if the action is completed or not.
I teach English.
Present tense – Past time, Present time, Future time
I wrote an article yesterday.
Past tense – Past time
If I sent the letter now, he would receive it tomorrow.
Past tense – Present time
If I sent the letter tomorrow, he would receive it the day after tomorrow.
Past tense – Future time
He learned English yesterday (complete).
He has been learning English (incomplete).