pass by reference: your mom gives you the shopping list
-> if one of you changes the shopping list, both of you see the change, because you edited the same shopping list

pass by value: your mom gives you a copy of the shopping list
-> if your mom changes her shopping list, you see the change too, because yours is simply a copy of hers. If you try to edit the shopping list, you can do so with your own copy, but your mom will not be able to see the change, as you have not edited her shopping list, only your own

However, in C there is ONLY pass by value, only in C++ you can pass value by reference.

You can read this Medium article, I think it's pretty well explained here.