[334x266]Sarah is in her car. She is on her way to work. 

She is driving to work.

This means: she is driving now, at the time of speaking. 

The action is not finished yet. 

Am/Is/Are + ing is the Present Continious.

I am doing someting = I am in the middle of doing it. I have started doing it and I have not finished yet:

• Please don`t make so much noice. I am trying to work.  (not I try).
• Where is Mark? He is having shower. (not He has a shower)
• Let`s go out now. It is not raining any more. (not It does not rain)
• (at a party) Hello, Jane. Are you enjoying the party? (not Do you enjoy)
• What`s all that noise? What`s going on? 

The action is not necessarily hapening at the time  of speaking. For example:

Steve is talking to a friend on the phone. He says:

[250x242] I am reading a really good book at the moment. It is about a man who...

Steve is not reading the book at the time of speaking. 

He means that he has started it, but has not finished  it yet. 

He is in the middle of reading it.

Some more examples:

• Kate wants to work it Italy, so she is learning Italian. (but perhaps she is not 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 Present Continious with today/ this week/ this year etc. (periods around now):

• You are working hard today. (not You work hard today)

We use the Present Continious when we talk about changes happening around now, espesially 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 am begining to enjoy it now. (not I begin)