Present Continuous (I am doing / I'm doing)

A - Check out this example situation:
        Dave is in his car. He is on his way to school.   
        He is driving to school.
        This means: he is driving at the moment of speaking, now. Indeed the action is not finished, rather is continuing.
        Am/is/are -ing is the present continuous:
                          I         am   (= I'm)                                  driving
           he/she/it          is      (= he's/she's/it's)              working
      we/you/they         are    (= we're/you're/they're)    dancing.

B - I am doing something = I'm in the middle of doing something; I've started doint it already and haven't finished at all.
        The action is often happening at the time of speaking or acting:

• Please don't make so much noise. I'm working a18 . ( not "I work")
• "Where's Lakisha?"   "She's having a bath."  (not "she has a bath")
• Let's go out now. It isn't raining any more. (not "it doesn't rain")
• (at a party) Hello, Jane. Are you enjoying the party? ( not "do you enjoy")
• I'm tired. I'm going to bed now. Goodnight!

         But the action is not necessarily happening at the time of speaking. For example:
       
                         
Dave and Lakisha are talking in a café. Dave says:
I'm reading an amazing book at the moment. I'll lend it to you when I've finished it.
Dave is not reading the book at the time of speaking.
He means that he has started it but not finished it yet.
He is in the middle of reading it.
   Some more examples:

• Lakisha wants to work in Barcelona, so she is learning Spanish. (but maybe she isn't learning Spanish exactly at the time of speaking)
• Some friends of mine are building their own house. They hope it will be finished before next summer.   

C - We use the present continuous when we talk about things happening in a period around now (for example, today / this week / this evening etc.):

• "You're working hard today."            "Yes, I have a lot to do." (not "you work hard today")
• "Is Lakisha working this week?"      "No, she's on holiday."

         We use the present continuous when we talk about changes happening around now:

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