See this page for more details on how to install MongoDB:
https://docs.mongodb.com/manual/installation/

$ sudo apt update
$ sudo apt install -y mongodb-org

Enable mongod server service:

$ sudo systemctl enable mongod.service
$ sudo systemctl start mongod.service

Check installation:

$ mongo --version

MongoDB shell version v4.2.0
git version: a4b751dcf51dd249c5865812b390cfd1c0129c30
OpenSSL version: OpenSSL 1.1.1  11 Sep 2018
allocator: tcmalloc
modules: none
build environment:
    distmod: ubuntu1804
    distarch: x86_64
    target_arch: x86_64

Configuration files:

• Binary file: /usr/bin/mongod
  
  
• Configuration file: /etc/mongod.conf
  
  
• DB path: /var/lib/mongodb/
  
  
• Log file: /var/log/mongodb/mongod.log
  

Start MongoDB as a service:

$ sudo service mongod start

Start MongoDB as a process using "config" paramter:

$ nohup /usr/bin/mongod --config /etc/mongod.conf &

Start MongoDB as a process using "dbpath" paramter:

$ nohup /usr/bin/mongod --dbpath /var/lib/mongodb &

Verify MongoDB status:

$ sudo service mongod status

Verify MongoDB process:

$ ps -ef | grep mongodb
mongodb   1517   /usr/bin/mongod --config /etc/mongod.conf

List active connections:

$ lsof -i | grep mongo

$ netstat -l | grep 27017

tcp        0      0 localhost:27017         0.0.0.0:*               LISTEN
unix  2      [ ACC ]     STREAM     LISTENING     1391442  /tmp/mongodb-27017.sock

Stop MongoDB:

$ sudo service mongod stop

Uninstall MongoDB:

$ sudo service mongod stop

$ sudo apt purge mongodb-org*
$ sudo apt autoremove

$ sudo rm -r /var/log/mongodb
$ sudo rm -r /var/lib/mongodb

Create a user/password on a specific database:

$ mongo

If you don't connect to a specific database, the user will be created on the "test" database:

> use mymdb

Create the user:

> db.createUser(
  {
    user: "user1",
    pwd: "pwd1",
    roles: [
      {
        role: "dbOwner",
        db: "mymdb"
      }
    ]
  }
)

Successfully added user: {
  "user" : "user1",
  "roles" : [
    {
      "role" : "dbOwner",
       "db" : "mymdb"
    }
  ]
}

Verify user creation:

> use mymdb
switched to db mymdb

> db.auth("user1", "pwd1")
1

Test user connection:

$ mongo -u user1 -p pwd1 mymdb

> db.getUser("user1")
{
  "_id" : "mymdb.user1",
  "userId" : UUID("59ace827-0b71-4674-a2cd-82ad6fd004d1"),
  "user" : "user1",
  "db" : "mymdb",
  "roles" : [
    {
      "role" : "dbOwner",
      "db" : "mymdb"
    }
  ],
  "mechanisms" : [
    "SCRAM-SHA-1",
    "SCRAM-SHA-256"
  ]
}

List all users of a database:

> use mymdb

> db.getUsers()

Delete a user:

> use mymdb

> db.dropUser('user1')

$ mongo

> use admin
switched to db admin

> show collections
system.users
system.version

> db.system.users.find()
{
  "_id": "mymdb.user1",
  "userId": UUID("b79c29e7-2ec8-41fa-924b-b08b6c33549d"),
  "user": "user1",
  "db": "mymdb",
  "credentials": {
    "SCRAM-SHA-1": {
      "iterationCount": 10000,
      "salt": "vb85F7h2TomgGGm7mw3ksw==",
      "storedKey": "rQ0GGHBN0affRBFGe3Wvm4Yrgfg=",
      "serverKey": "yKnztyYNJW15tH/nBte/h01tD0A="
    },
    "SCRAM-SHA-256": {
      "iterationCount": 15000,
      "salt": "yPFiaRmV9ffKw7iZU+ROP/uLVb1w9/X1lwrF4A==",
      "storedKey": "5Mlt6bA9p6dP+xch5hI6NItes0fmyHF9lIiYu5euXgs=",
      "serverKey": "a1Hwo5Cyc8E6vQGDpqxR1wRLuSZ6qEU3VCeZAh8QH3M="
    }
  },
  "roles": [
    {
      "role": "dbOwner",
      "db": "mymdb"
    }
  ]
}

> db.system.version.find()

{ "_id" : "featureCompatibilityVersion", "version" : "4.2" }

$ mongo

> use mymdb

> db.createCollection("mycollection")

> show collections
mycollection

> db.mycollection.find({},{_id:1})

> db.mycollection.find()

> db.getMongo()

> show users
> db.getUsers()
> db.getUser("user1")

> show roles

> db.dropUser("user1")

> show databases
> show dbs
> db.getMongo().getDBNames()
> db.adminCommand("listDatabases")

> use mymdb
> db.getName()

> db.dropDatabase()

> show collections
> db.getCollectionNames()
> db.createCollection("mycollection")

> show tables

> db.mycollection.find()
> db.mycollection.findOne()
> db.mycollection.find().limit(10)
> db.mycollection.count();

> db.mycollection.dataSize()
> db.mycollection.storageSize()
> db.mycollection.totalIndexSize()
> db.mycollection.totalSize()

> db.printCollectionStats()
> db.mycollection.stats()

List databases:

$ mongo --quiet --eval  "printjson(db.adminCommand('listDatabases'))"

{
  "databases" : [
    {
      "name" : "admin",
      "sizeOnDisk" : 176128,
      "empty" : false
    },
    {
      "name" : "config",
      "sizeOnDisk" : 110592,
      "empty" : false
    },
    {
      "name" : "local",
      "sizeOnDisk" : 73728,
      "empty" : false
    },
    {
      "name" : "mymdb",
      "sizeOnDisk" : 8192,
      "empty" : false
    }
  ],
  "totalSize" : 368640,
  "ok" : 1
}

List collections names of a specific database:

$ mongo -u user1 -p pwd1 mymdb --quiet --eval  "printjson(db.getCollectionNames())"

[ "mycollection" ]

Configuration file: /etc/mongod.conf

# network interfaces
net:
  port: 27017
  bindIp: 127.0.0.1,192.168.2.33  # Comment to listen on all interfaces.

security:
  authorization: enabled

Test connection:

$ mongo --host localhost --port 27017 -u user1 -p pwd1 mymdb

Remove mongodb-org package: Uninstall MongoDB

Remove the existing mongodb.list:

$ sudo rm /etc/apt/sources.list.d/mongodb*.list

Create the MongoDB repository list file:

$ echo "deb [arch=amd64] https://repo.mongodb.org/apt/ubuntu bionic/mongodb-org/4.2 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-4.2.list

If you execute the command "apt update" you might get the following error:

W: GPG error: https://repo.mongodb.org/apt/ubuntu bionic/mongodb-org/4.2 Release:
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 4B7C549A058F8B6B
E: The repository 'https://repo.mongodb.org/apt/ubuntu bionic/mongodb-org/4.2 Release' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.

So first, you need to add the MongoDB key:

$ sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv 4B7C549A058F8B6B

Executing: /tmp/apt-key-gpghome.r2EHiLZD0B/gpg.1.sh --keyserver hkp://keyserver.ubuntu.com:80 --recv 4B7C549A058F8B6B
gpg: key 4B7C549A058F8B6B: public key "MongoDB 4.2 Release Signing Key <packaging@mongodb.com>" imported
gpg: Total number processed: 1
gpg:               imported: 1

Install MongoDB:

$ sudo apt update
$ sudo apt install -y mongodb-org

You can find the MongoDB puclic key ("4B7C549A058F8B6B") by visiting the Ubuntu key server http://keyserver.ubuntu.com

• Enter the "OpenPGPkeyserver": MongoDB
  
• Click "Search Key".
  
• In the search result page, find the version "4.2" and look for the last up-to-date key.