He is driving to work.
This means: he is driving now, at the time of speaking. The action is not finished.
Am/is/are – ing is the present continuous :
I am doing something = I’m in the middle of doing something; I’ve started doing it and I haven’t finished yet. Often the action is happening at work at the time of speaking:
Please don’t make so much noise. I’m working (not I work)
‘Where’s Suttipon?’ he’s taking a shower (not he takes a shower)
Let’s go out now. It isn’t raining anymore. (not it doesn’t rain)
(at a party) Hello Pawida. Are you enjoying the party? (not Do you enjoy)
But the action is not necessarily happening at the time of speaking. For example:
Suttipon and Pawida are talking. Suttiporn says:
I’m reading an interesting book at the moment. I’ll lend it to you when I’ve finished it.
Note: Suttipon 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.