A lot of people will conjure up vibes-based meanings for those words that end up being arbitrary or vague, but it's actually pretty straightforward. Fetish-worship started as religious practice that incorporated specific symbology. Christ on the cross, temples of Athena, a statue of the buddha - all of those would be fetishes. For sexuality it's the same deal. A fetish involves a specific material thing that gets you aroused. Leather, high heels, maid outfits, fireman uniforms and things along those lines would all be fetishes. Another way to think of it is that the thing in itself can be hot to you regardless of the context. It's your own libido that sexualizes it.
Kinks are more psychological. If there's a specific scenario that triggers an intense arousal in you then that would be a kink. With a kink the whole performance is explicitly sexual, so all the details are dedicated to telling the exact erotic story that gets you off. Unlike a fetish where the trigger needs to be physically present, kinks can play out entirely within someone's imagination. If the line ever feels vague, just ask yourself whether the circumstances are what's important (probably a kink) or the physical presence of some particular thing is important (probably a fetish).
And that's really all there is to it.