Creating admin user and new database in mongodb

To create admin user open mongo shell and do 

use admin
db.createUser(
  {
    user: "myUserAdmin",
    pwd: "abc123",
    roles: [ { role: "userAdminAnyDatabase", db: "admin" }, "readWriteAnyDatabase" ]
  }
)

To create database named Collection0 open mongo shell and do 

db.createCollection( "Collection0") 

To see databases do

show dbs

To see tables do

use <database_name> 

show collections