When and how to use weapon tags

I am new to this system and I was wondering when and how you use certain weapon tags.
When do you tell a player that he needs to reload? Or how does a heavy weapon influence play? Does a player with a heavy or a slow weapon simply go last in a fight? If a weapon sets things on fire - how do you deal with that? Does the fire cause harm until you put it out? How would you put it out - with "Act under pressure" or would you just let the player tell you how he puts it out? Many questions... I know!
The unreliable tag is another one I am not sure about. Do you just tell a player that this time the weapon does not work?
Maybe I have missed something but some general advice on this would be very helpful!
Thanks in advance!

They're hints for the fiction, so you can use them in a lot of ways. Think of them as suggestions to help you decide what Keeper move to use.

In general, you wouldn't just tell a hunter with a "reload" weapon that it's out of ammo, but on a 7-9 result maybe that's something that goes wrong, or on a 6 or less maybe they just shot the last bullet.

Thank you very much, Mike!