Hello,
it is normal to add a tip or the so-called service fee as you pay for services like taxis and eat in restaurants or visit a confectionary or coffee-house. That is the theory. The real-life experience is that a very high percentage of restaurants and confectionaries add the service fee which often varies between 10% and 15% directly to the bill, meaning that it is already included. In such cases, you shouldn’t add anything on top of the amount you see on the bill. This is normally showing up on the bill as service fee (with a percentage behind). You can also look in the menu beforehand as it will normally be told you there if the service fee is included or not on the final bill.
If you visit a hairdresser, you can add a tip at the end (the hairdresser will be very happy).