When you start with electronics, you'll hear a lot about power supplies - they're in every electronics project, and they are the backbone of everything! A good power supply will make your design hum along nicely. An inadequate power supply will make life disappointing: stuff will work sometimes but not others, inconsistent results, motors not working, sensor data always off. Understanding power supplies (boring though they may be) is key to building your project work!
A lot of people don't pay much awareness to power supplies until problems show up. We think you should always think about your power supply from day one - How are you going to power it? How long will the batteries last? Will it overheat? Can it get damaged by accidentally plugging in the incorrect thing?
Power supplies are all around you!
Unless you live in a shack in the woods, you probably have a dozen power supplies in your home or office.