Study this example situation:

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.

______________________________________

Am / is / are + Ving 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 Michael?' 'He's having a shower. (Not He has a shower)

Note: 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 time of speaking.

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