PRESENT CONTINUOUS
IT IS USED TO EXPRESS A TEMPORARY ACTIVITY THAT IS IN PROGRESS AT THE MOMENT OF SPEAKING:
I am listening to the radio now.
It is raining at the moment.
They are reading. Please, be quiet!
IT IS USED TO DESCRIBE A TEMPORARY ACTIVITY IN PROGRESS THAT OCCURS IN A CERTAIN PERIOD OF TIME (TODAY, THIS WEEK, THIS MONTH, THIS YEAR, THIS TERM):
Martin is trying to lose excess weight this year.
I am writing a letter of application for a university today.
She is staying at her friend's place this week.
IT IS USED TO DESCRIBE AN ACTION THAT IS CHANGING OR DEVELOPING:
It is getting dark
The crowd is getting louder
IT IS USED TO EXPRESS ANNOYING HABITS:
You are always leaving the doors open.
They are having parties in the middle of the week all the time.