The Raspberry Pi board (many versions) is usually the next step up from an Arduino for most robot builders and requires a fair bit more computer understanding.
They both serve different purposes however and the Arduino is usually the best choice when adding servos and sensors for most robot projects but it is only a microcontroller while the Raspberry Pi is more like a full blown computer that can run an operating system.
When you need to do the advanced things like setting up stereo cameras with technology like OpenCv and almost anything involving some level of artificial intelligence you’ll probably be working with a Raspberry Pi using an operating system like Ubuntu or Raspbian.
There are quite a few great websites to help new and advanced users with their Raspberry Pi issues. Here is one such link Howchoo. howchoo.com/