We use this for things in general or things that happen repeatedly
Water boils at 100 degrees celsius.
Excuse me, do you speak English?
It doesn't rain very much in summer.
What do you usually do at weekends?
I always get hungry in the afternoon.
Most people learn to swim when they are children.
We use this for things hapening at or around the time of speaking.
The water is boiling. Can you turn it off?
Listen to them. What language are they speaking?
Let's go out. It isn't raining now..
I'm busy. What are you doing?
I am getting hungry. Let's go and eat.
I want to work in Italy. That's why I am learning Italian.