One nice thing about the iPhones is that they stay quite consistent in how to use them.
(I've been using em for nearly 10 years and the look and feel of the user interface is pretty much the same)
The iPhone 8 will use the same iOS as the new iPhone 12.
The only major difference being Touch ID vs Face ID, which is the biometrics you can use to unlock your phone
Here is a link to the user guide for the iPhone. This applies to your iPhone 8 as well as to the newer phones
iPhone User Guide - Apple Support
If you want to find videos specifically, you'd be better off Googling the topic and finding YouTube videos