Azure Cosmos DB emulator is to implement and test the applications using Cosmos DB even without the Cosmos DB account. We don’t need an internet connection to build the applications by running the Cosmos DB emulator locally. You do not need any subscription to Azure or Cosmos DB account to develop applications. We can develop and deploy applications to the cloud without any extra cost.
In case you are interested to learn Azure Cosmos DB, I recommend you to take up this Azure Data Factory training by Intellipaat.
You can watch this video on Azure Cosmos DB tutorial to know about Azure Cosmos DB emulator: