To list mongodb database on shell
show databases //Print a list of all available databases.
show dbs // Print a list of all databases on the server.
Few more basic commands
use <db> // Switch current database to <db>. The mongo shell variable db is set to the current database.
show collections //Print a list of all collections for current database.
show users //Print a list of users for current database.
show roles //Print a list of all roles, both user-defined and built-in, for the current database.