With a Raspberry Pi, you can use it as a microcontroller but also as a computer that can run an OS. So it’ll have things like networking, display outputs, but also have pins to connect devices to. You program a Pi with Python.

An Arduino is more a microcontroller in the classical sense. It doesn’t run an OS, but rather the program you send to it, and that’s it. It’ll run that program forever. The programming language (or library as some refer to it) is more akin to C++.

EDIT: I should note that an arduino can have peripherals and things like networking too, but you’ll need to buy “hats” as they’re called. They sit on top of the arduino, extending the pins but also giving you extra functionality.

So I would say that if you’re explicitly trying to use Python, a Pi is the way to go. That said, there are toooons of guides out there with say “10 Raspberry Pi Projects for Beginners”. Sometimes Humble Bundle has bundles with those kinds of books.

Get yourself a kit online with basic components if you don’t have them already. And maybe a breadboard. Just dive in. Don’t overthink the projects in the beginning. Just try the easy stuff till you understand enough that you can try making your own devices.