You first encounter the Stormterror dragon in Genshin Impact during the first part of the game. Throughout the story, you learn that Stormterror's name is Dvalin, a dragon of the Four Winds. Before you encounter Stormterror for the first time, make sure everyone in your party is at least level 26. This is your first time fighting it. In higher level meetings, this recommendation level increases to 40, 50, 60, 70, 80 and 90.
During the first part of the fight, you learn that the blood clots on his back are what corrupted him. You have to aim for these while hovering in the air, like when you first encountered Stormterror when you first started the game. Shoot the blood clots until Stormterror flies out of range, then dodge attacks that hit you until it gets closer. Look for the crystal blue balls of light to shoot to create a ring of wind. These have a health bar on them. Dash through to catch Stormterror and shoot the blood clots when you get close enough.
After reducing Dvalin's health, there is a brief cutscene, and then you have to fight her on the field. You want to use Venti, which is available for a trial, during this fight. The dragon will rush over to the platform you are using, so be sure to dive to the sides to avoid this attack.
When Dvalin tries to bite, dodge, then charge up Venti's attack and shoot the blood clot on his neck. Hitting him with basic attacks is also acceptable. You have to wait until the upper part of his neck is exposed. When you lower Dvalin's white health bar, his head drops and you can rush to attack the blood clot on his neck.
Once you lower Dvalin's health enough, energy will begin to flow from the platform and a gust of wind will appear on the platform. Use it to move on to the next one until you reach a place where it doesn't look like it's about to break and explode under you. When you're safe it comes down to attacking Dvalin and dodging his attacks.
You'll likely reach the point where Stormterror is almost out of health before another white bar appears. Hit it a few more times and it should drop pretty quickly. When it falls, you will have completed the battle, and a cutscene appears.
