Theory:

In English, verbs are used to describe THE PRESENT, THE PAST and THE FUTURE.
These are called TENSES.

There are three kinds of verbs:
I PLAY tennis - PLAY is an action verb.
I AM happy - the verb TO BE is used to describe a condition.
This food TASTES good - TASTES is used as a linking verb.

We will look at the PAST, PRESENT and the FUTURE with action verbs.

THE PRESENT

There are two ways of talking about the present.
There is something you do regularly.
For example:
I always play tennis - (called the PRESENT SIMPLE)
This in the NEGATIVE and QUESTION form uses DO and DOES.

There is something you are doing right now.
For example:
I am playing tennis at the moment. - (called the PRESENT CONTINUOUS)

Any action happening now is considered to be TEMPORARY.
Any action that always happens is considered to be PERMANENT.
So one characteristic of CONTINUOUS TENSES is that they are TEMPORARY.

The infinitive form of the verb play is TO PLAY

The present simple uses this form without the TO
For example:
I always PLAY tennis.

The present continuous uses this form, without the TO and + ING and the verb TO BE.
For example:
He is playing tennis now - IS (TO BE) + PLAY + ING.