What is he doing?
He's driving.
What is she doing?
She's eating watermelon.
What is she doing?
She's running.
What is he doing?
He's watching TV.
What are they doing?
They're cooking.
What is she doing?
She's reading.
What are they doing?
They're studying.
What is he doing?
He's playing soccer/football.
What are they doing?
They're swimming.
What is he doing?
He's singing. / He's playing the guitar.