Azure Cosmos DB is used in building mobile applications for modeling social interactions and for personalized features. Also, Cosmos DB is used to build applications for communication and interactions with friends, family, and people with similar interests. Cosmos DB is used in the gaming field to reach your product to more regions than your competitor. Cosmos DB is used in retail also for storing catalog files like user accounts, product catalogs, etc. and processing pipeline of events. Cosmos DB helps in the IoT field to handle IoT devices from any location using the cloud.
If you want to learn Azure Cosmos DB, I strongly recommend enrolling this Azure Data Factory training by Intellipaat.
You can watch this video on Azure Cosmos DB tutorial to know about how different fields use Azure Cosmos DB: