Your question is a bit ambiguous, but I will endevour to answer your question. If you are referring to "What are charms used for?" then the answer is the summoning skill where you can summon pets (or familiars) to aid you in a variety of ways. To begin to train summoning you have to have completed the wolf whistle quest. A very useful and informative guide on summoning can be found on the runescape website under manuals.
You get charms by monster drops.
No, you have to kill monsters like cockroach soldiers to get charms.
enough.
Sorry but I'm afraid you cant re-use gold charms on Runescape, but however you'd be glad to know they are stackable.
Slayer usually gets it
Waterfiends.
The best place to get crimson Charms would be killing the high level cockroaches at the player safety dungeon.
Almost every Monster Drops Gold Charms but you can receive multiple charms from the level 111 Giant Rock Crab in the Chaos Tunnels.
If it's charms you are after, you best go to the Chaos Tunnels, look for the "Giant Crab", that usually drops multiple charms.
When I trained range on fire giants i got like 100 blue charms or more their not likely to appear though that's just one of the monsters that drop them try going to a runescape help site and type in monsters that do drop blue charms.
I would say an Ibis is the best way to level summoning in terms of Shards used and exp given.
yes they are if you note them. They are stackable even if you don't note them.