Wall for Chaos481 (page 20)

Thing is, you gacha to get playable cgaracters and weapons in Genshin. Some weapons are craftable, however some others, usually the ones specific to a character (Like Eula's claymore), are not craftable. You use these Primogems to pull a gacha.

You gacha in these things called "banners" that you can access via the menu when you play. Banners are available for a very limited time (usually 3 weeks ~ 1 month-ish) except the beginners banner where you can gacha this character called "Noelle" and the standard banner. Every once in a while, a new banner will be put up, featuring new or characters that has appeared somewhere in the past. Banners featuring characters that has been featured in the past are called "reruns".

Specific weapons have their own banners, however common weapons can be obtained in the characters' banners.

The gachas has this system called "pity" that will determine whether you get a 5☆ character or not (or something around that lines), however a pull for the first time has something called a 50/50 system, which means there is a 50% chance you'll get a 5☆ and another 50% that you won't.

5☆ are usually the characters featured in the banner you are doing your gacha pull in. They are usually the one positioned in the front of the banner art. There will be a few more characters behind them, they are usually the 4☆ you can obtain.

Each pull costs 160 Primogems, however 10x pulls will cost 1.6k Primogems. In most banner, it is guaranteed that you will get a 4☆+ character or weapon If you do the 10x pull.

Fwee, thats long! Tl;dr: You use Primogems to get characters and weapons :)