Okay, so think about when you breathe in air. Your lungs take in oxygen from the air and give it to your body to use. But sometimes, your lungs can have a hard time doing this.
This is where theophylline comes in. It's a medicine that can help your lungs work better.
Imagine your lungs are like a bunch of little balloons. When you breathe in, they fill up with air. But sometimes, they can get too "tight" and it's hard for them to let the air in and out.
Theophylline helps relax the muscles around those little balloons so they can open up more and let the air flow better.
So basically, theophylline is a medicine that can help you breathe better if your lungs are having a hard time doing their job.