The database is the container for collections. It has its own sets of files on the file system and a single MongoDB instance can have multiple databases.
MongoDB stores documents in collections. Collections are analogous to tables in relational databases. One of the benefits of collection compared to tables is that they do not enforce a schema and Documents within a collection can have different fields.
Documents in MongoDB are equivalent to the rows in relational databases. Data is stored inside the documents in a set of key-value pairs and documents have a dynamic schema.
join statement on RDBMS databases MongoDB has a similar concept that is used to related documents and joined them. Embedded documents help to mimic the