Legitimate Apple-approved site for training

While it appears to be meant as training modules for Apple employees, you can learn a lot about Apple products on their own tutorial site:

https://it-training.apple.com/support/tutorials/course/#getting-started

No, it is not “Apple approved”.

Apple has several legit sites to learn about Apple devices. For example:

https://www.apple.com/today/event/get-started-iphone/7424111012162666496/?sn=R077

Are you looking for training in using Apple products, or training to be an Apple service/repair provider? They are very different.