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 + 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 yet:
Please don’t make so much noise. I’m trying to work. (not I try)
“Where’s Mark?” “He’s talking 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, Jane. Are you enjoying the party? (not Do you enjoy)
What’s all that noise? What’s going on? (=What’s happening?)
The action is not necessarily 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.
He is in the middle of reading it.
Some more examples:
Kate wants to work in Italy, so she’s studying Italian. (but perhaps she isn’t studying Italian at the time of speaking)
Some friends of mine are building their own house. They hope so 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 enjoy it now. (not I begin)