"/" means divided by.
Where you put variables is something you will get if you just dig in and start using construct. The clue is mostly in the names but there is some flexibility in how to use them.
Instance variables are variables related to object instances. Player health, enemy shield ect and much more.
Globals are for things that are not related to object instances or are numbers that need to be allways available to the game. ( But as you can see there is nothing stopping you put things you might deem global into an object instance (or vice verser) but if that instance is destroyed then those variables won't be available. (and a global variable is no good if you want to have different values for different instances of an object).
Locals are places to store for small sections of code under an event or function, maybe to hold values while other calculations are performed. Or just to provide values for that section of code. Once the code moves onto the next event these variables essentially do not exist and can't be used by other parts of code. They can be initially set and will retain their value for the next time if you make them static.
You'll get it after a bit....at the end of the day variables are just places to hold numbers or letters,
Although they each perform slightly different roles there are really no hard rules to observe (someone will probably kill me for saying this). but IMO, Its really about whatever works for your game.
to make even more interesting you can store and retrieve variables to/from dictionaries and arrays and probably other things I havent discovered yet.