The reason you end up with 'arrive to' in that sentence though isn't because you're using it instead of 'arrive at'. There's 3 parts to that sentence that you can put in any order potentially. There's 'I arrived', there's 'At the soup kitchen', and there's 'To serve hot meals'.
In your second...
Honestly it's probably easiest for them to learn by playing and seeing other GMs do it, then getting some direct advice from them to start.
I think it's hard to learn totally from scratch via online resources.
It sorta depends on the thing right? Not all rules are made equal.
Something like a character ability I probably won't touch for a while until it becomes very obvious it just doesn't work right, and I'll start by going online to see what other people have done about the issue.
Something like...