A. There are two tenses in English: present and past.
B. The present tenses in English are used:
B1. to talk about the present (e.g. London is the capital of Britain.)
B2. to talk about the future (e.g. You will be tired out after you have been working all night.)
B3. to talk about the past when we are telling a story in spoken English or when we are summarising a book, film, play etc. (e.g. He’s having problems with the car again.)
C. There are four present tense forms in English:
C1. Present simple (e.g. I work.)
C2. Present continuous (e.g. I am working.)
C3. Present perfect (e.g. I have worked.)
C4. Present perfect continuous (e.g. I have been working.)