Problems with youtube tutorials

I dont know if other people have issues understanding tutorials as well, but I have a lot. It’s very frustrating, I feel too much information is held back. They add variables, hook up nodes, and often it just misses explanation of where they get their values from how they work together etc. and I cannot understand the whole picture.

Like for instance in this picture here,
he created a variable in the firstperson Bp called inventory, where he saves values. All fine here for me.
But then he creates another variable called ItemStacking1p, and I dont get where this variable gets its values from. he doesn’t say what it does and where it gets its values from.


and whole chain goes further and i totally lose track.