The error "port 8081 is already in use" comes in Azure Cosmos DB Emulator as by default azure cosmos db emulator uses the Port 8081.
So to fix this issue of "port 8081 is already in use" , we have to change the port number and to do so go to the location where Azure Cosmos Local Emulator is installed. By Default the location is
"C-Program Files-Azure Cosmos DB Emulator"
Here Run the Command
This would change the port number to 8084 and after this you would be able to access the Azure Cosmos Local Emulator in browser locally.
Also this issue has been explained in above video, you can have a look here.
Also If you are interested in learning Azure Cosmos DB with scratch - you can visit to our azure cosmos db tutorial playlist in YouTube
Here we have explained What is azure Cosmos DB, How to create collections, documents in Azure Cosmos db Also what throughout in Azure cosmos db and what is Partition key, all this have been explained with practical example