PRESENT CONTINUOUS TENSE

A. We use the present continuous when we talk about something which is happening at the time of speaking.

Formulas : (+) Subject + tobe ( am/is/are) + Ving

                 (-) Subject + tobe ( am/is/are) + not + Ving

                 (?) Tobe (am/is/are) + Subject + Ving

•  Please don't make so much noise. I'm studying. (not ' I study')
• "Where is Ilma?" "She is having a bath." (not 'she has')
• Let's go out now. It isn't raining any more.
• (at a party) Hello, Lia. Are you enjoying the party ? (not 'do you enjoy')

B. We also use the present continuous when we talk about something which is happening around the time of speaking, but not necessarily exactly at the time of speaking. Study this example situation:

• Lia and Vera are talking and drinking in a cafe. Lia says: "I'm reading an interesting book at the moment. I'll lend it to you when I've finished it."

Lia is not reading the book at the time of speaking. She means that he has begun the book and hasn't finished it yet. She is in the middle of reading it. Here are some more example:

• Susy is learning is at the moment. (not 'learn')
• Have you heard about Lia ? She is building her own house. (not 'builds')

But perhaps Susy and Lia not doing these things exactly at the time of speaking.

C. We often use the present continuous when we talked about a period around the present. For example: today, this season, etc. :

• "You're working hard today." "Yes, I have a lot to do."
• Adam isn't playing football this season. He wants to concentrate on his studies.

D. We use the present continuous when we talk about changing situations :

• The population of the world is rising very fast. (not 'rises')
• Is your English getting better? (not 'does ... get')

Read more: English Grammar in Use_Raymond Murphy