How do I save global variables using Local Storage?

Hi guys! So the game I'm building relies pretty heavily on global variables for a number of tasks, such as changing playable characters, tracking progression through the levels for each individual character, and saving the high scores for each character as well.

The variables work perfectly, but I'm wanting to use Local Storage to save them and I'm finding it incredibly complicated and fiddly! Can anyone help me find a simple solution that can be used to save and retrieve the assorted global variables? I would be incredibly grateful, thank you in advance!

Oh, I forgot to mention that in many instances I am needing to save or retrieve the information from multiple global variables at a time! For instance, at a given checkpoint I need to save "Character A Level Progress", "Character A Score", and "Character B Unlocked". I'm not sure if that changes anything or makes things more difficult!

Again, thanks for your time!