My sql server database table has Guid as primary key (Id) column and default as newid(), when making an insert to the table using entity core, if i dont supply the Id field i would like the insert ...

If you are asking “GUI-what?”, not to worry, you aren’t alone. A GUID is a Globally Unique Identifier that helps manage the relational data in the Common Data Service for Apps and SQL Server.

The traditional GUID (a.k.a UUID Version 4) is fine and works really well for it's intended use. But its random nature is problematic in some scenarios that's why other UUID versions have been created ...