Tenses and their use

How many tenses are there and what are they?: Tenses are three types:

1. Present tense

2.Past tense 

3. Future tense

In each tense there are four sub categories. They are:
1.Simple
2. Continuous
3.Perfect
4. Perfect continuous

Now we shall discuss each tense clearly

1. Present simple or simple present: This tense is used to describe habitual actions and universal truths.
structure.
Structure: subject+verb1+ object
Ex1. sun /rises/ in the east(universal truth)

Here sun is subject, rises is first form of verb and in the east is object.
Ex 2. He/ walks/ daily in the morning( habitual action)

Ex3. Earth/ revolves/ round the sun

First person singular (I) and second person singular(you) uses just verb for example read, write, speak...etc and third person singular adds "s" to the verb.
 Ex. She eats, he drinks, it happens.