There's two types of crystals, anemos crystals and protean crystals. these are used for your upgrades with gerolt for your level 70 relic gear

You get the former by doing fates, which are spawned by mass murder of certain mobs when their window is up. The latter you can get by chain mobs or exchanging the former for protean with gerolt at a rng rate

Best advice: join a fate train and ask around

You get to the next map at level 20 and completing all the story quests. Then you are in the worst of the maps for eureka