Please explain how gold/item find and XP gain work

Please explain how gold/item find and XP gain work

I found the descriptions of "Thief gloves" and "Relic Hunter's Ring" rather obscure: "Increase gold/item find by 25 (or something like that)". 25... what, exactly? Percent? Some arbitrary flare-internal unit? If so, how skilled is my character at finding gold/items to begin with? Do they affect how often mobs, crates, barrels, minecarts, treasure chests drop gold/items? Do they affect the amount of gold/the quality of the items?

Pretty much the same questions apply to the XP gain effect: Does it add, multiply or exponentiate the XP I gain? Or something else? Does it affect XP gained from quests? Does it affect XP gained from killing mobs?