Check out example codes for "drop mongo database". It will help you in understanding the concepts better.

Code Example 1

// First show what databases have you gotten 
show dbs
// then, use the database name that you want to drop
use YOUR_DATABASE_NAME
// now you can drop it
db.dropDatabase()
// show collections should be empty now
show collections

Code Example 2

use DB_NAME       // go to the db you want to delete

db.dropDatabase()

show dbs
// droppped db will not be shown

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