Study this example situation:

Am/is/are+ -ing is the present continuous:

I am doing something= I'm in the middle of doing it; I've started doing it and I haven't finished:

• Please don't make so much noise. I'm trying to work. (not I try)
• 'Where's Mark?'    'He's having a shower.' (not He has a shower)
• Let's go out now. lt isn't raining any more. (not lt doesn't rain)
• (at a party) Hi, jane. Are you enjoying the party? (not Do you enjoy)
• What's all that noise? What's going on? (=What's happening?)

Sometimes the action is not happening at the time of speaking. For example:

Steve is talking to a friend on the phone. He says:
I'm reading a really good book at the moment. it's about a man who ...

Steve is not reading the book at the t ime of speaking.
He means that he has started it, but has not finished it yet.
He is in the middle of reading it.

• Kate wants to work in Italy, so she's Learning Italian. (but perhaps she isn't learning Italian at the time of speaking)
• Some friends of mine are building their own house. They hope to finish it next summer.

You can use the present continuous with today / this week / this year etc. (periods around now):

• A: You're working hard today. (not You work hard today)
  B: Yes, I have a lot to do.
• The company I work for isn't doing so well this year.

We use the present continuous when we talk about changes happening around now, especially with these verbs:

• get  change  become   increase  rise fall
• grow improve  begin  start

• Is your English getting better? (not Does your English get better)
• The population of the world is increasing very fast. (not increases)
• At first I didn't like my job, but I'm beginning to enj oy it now. (not I begin)