As far as teaching someone the basics about blocking in another fighting game, such as a 2D one that you’re describing, the only reason you don’t really start talking about strike/throw mixup defense is because it’s more difficult to perform. You’re talking about teching throws with a very specific timing window when the player doesn’t even have a grasp of the basic rhythm of fighting games yet.
Here, you know to block by default. Period. Let go when you think they’ll throw. You don’t have to worry about buffering any type of teching in a block string. This also has the immediate feedback of “Oh, I got hit here” or “Oh, I got thrown here” when they’re starting to choose how to defend. Immediate feedback of what they did right/wrong is the most important part of learning how to adjust. Most fighting games give you seemingly ambiguous feedback, until you start actually learning about the engine itself, as far as trying to block mixups.
As far as doing mixups, it follows very simply in concept from there. Performing the mixup requires practice, but the concept itself is not difficult.