Well, we use the Present Continous tense when we talk about something that is happening at the time of speaking (Cambridge - English Grammar in Use).
Example:
- Please don't make so much noise! I'm studying (not I study)
- "Where's Peggy?" " She's taking a bath" (not takes a bath)
- Let's go now. It isn't raining anymore.
- Tom and Ann are talking and having coffee in a cafe. Tom says,"I'm reading Twilight at the moment. I'll lend you as soon as I finish reading it" (not read)
- Have you heard about Brian? He's building his own house (not builds)
- You're working hard today.
- Tom isn't playing football this season. he wants to concentrate on his study.
Example:
- Is your father's condition getting better?
- The population of the world is rising very fast.