Here you can read what Charms are in Diablo Immortal. You will learn how to craft them, salvage and give them the specific characteristics.
What are charms?
You will unlock access to charms at level 56. However, you can find them earlier - but before reaching that level, store them in the Stash. You can only have one charm at a time, but you can upgrade it up to level five. Each level adds an attribute to the item that boosts a random skill. The problem is that this is a random skill picked from all of the in-game skills, not just your character class.
How to modify a charm?
To raise a charm's level, you need to use the powder that you get from salvaging talismans. You will do this at the Charm Craftsman in Westmarch. You can only salvage rank 1 charms. If you upgrade it, you have to keep upgrading it up to level 5 to be able to perform Extraction or Infuse on it. To work on a level 5 charm, you first have to remove it.
You can do two things: Extract and Imbue. Extract allows you to obtain a random buff from a level 5 stone and turn it into a Skill Stone. Unfortunately - this costs 500 Platinum. Such a stone has all the skills of the charm. You can sell Skill Stones on the market. Therefore, you can also buy them (for Platinum) to build a good stone faster.
The next stage of stone modification is Imbueing. By using Skill Stones (purchased/crafted), you can exchange one of the skills in the currently used charm for a random from a Skill Stone. Because of that creating the perfect charm is difficult.
After switching skills, you can additionally decide whether you want to accept the new skill or keep the old one. Thanks to this, you will not waste a good charm. The skill can only take up one slot per charm, even if it has a different buff percentage.
The important thing is that when you use Skill Stones to modify a charm, an ability taken from a Skill Stone will receive a 2-10% skill boost bonus, when the charm has that skill on at lest at 2% by default.
How to get charms?
One method is to buy charms from the Hilt Merchant. Although he has a weekly limit of 3 pieces, he often has an additional piece for time-limited offers that you can check every day. The second option is the Battle Pass - you can get an additional charm from time to time. It is very unlikely that you can get them for completing Bounties, but you have no guarantee here.