1. There are two tenses in English mainly Past and Present. The present tense in English are used

• to talk about the present
• to talk about the future
• to talk about the past

There are four present tense forms in English.

Present simple                  Example : I play

Present continuous           Example : I am playing

Present perfect                 Example : I have played

Present continuous           Example : I have been playing.

In the simple present tense, we normally use the root form of the verb. But with he, she it and other third person singular subjects we have to add -s or -es to the root form.

Where to use the simple present tense.

1. The main use of the simple present tense is to express actions as a matter of habit or action done repeatedly.

Parrots eat nuts. (habit)

He goes for long walks. (repeated action)

2. Present tense expresses scientific facts and permanent truths.

A magnet attracts iron.

Yoga exercises keep us fit.

Words often used with present tense are always, never, usually, generally, seldom etc.

I always go to temple on Sundays.

We generally spend our evenings at home.

3. The tense is also used to express natural qualities and professional activities.

Honey tastes sweet. (Natural quality)

A chemist sells medicines. (professional quality)

4. Simple present tense used in proverbs also.

A stitch in time saves nine.

Present continuous tense

1. The present continuous tense denotes an action taking place at the time of speaking.

Example. It is raining now.

2. It is used to denote a temporary action, which may not be necessarily happening at the time of speaking.

Example: These days I am revising my courses.

3. Words like now, today etc are used with the present continuous tense.

Example: It is raining heavily today.

Verbs not normally used in present continuous tense.

4. See, look,, hear, listen

see and hear are non action verbs. While look and listen are action verbs.

Example: I see a man outside
                He is looking at me.

Have:
Have shows possession or conditions. We should not use it in the present continuous tense.

          But we can use have in the present continuous tense in these two cases [When have refers to some arrangement for the future]

Example: We are having a party tomorrow.
                He is having his bath.