With so many information available, it’s sometimes hard to figure out where to start best. Are the tutorials you are using complete enough to get started properly, yet simple enough not to get lost as a newbie? Allow me to point you in the right direction.
For the Arduino there is a great tutorial, where it really starts from the very beginning like: “What is an Arduino?” to the more advanced stuff like interrupts. Every chapter is supported with source code, schematics and a video.
Also from Core Electronics, the tutorial the provide for the Raspberri Pi really start from the very beginning, and takes it all up to creating your own GUI’s and IOT.
You can find it at at Core Electronics: Raspberry Pi Workshop for Beginners
There’s also a playlist available.
If you’re more into reading, the Raspberry Pi Beginner’s Guide is also available from the Raspberri Pi website.
The Raspberri PI runs on a (special) linux distribution. If you’re looking for a good linux tutorial, well, I’m not sure either where a good start would be. I learned it from a series of a books called: SAMS Teach Yourself Linux
and they have worked great for me on several IT topics. You can still find them on amazon.
Since most projects for the Raspberri PI, when it comes to I/O, are scripted in Python, it’s a good idea to start there if you’re going to write your own programs.
There is a very good video tutorial available here: Python Tutorial for Beginners [Full Course] 2019