database.yml is configuration file which tells rails about database, database information.

database.yml

# MariaDB version 10.1
  # Install the MySQL driver:
  #  gem install mysql2 --no-ri --no-rdoc
  #
  # Ensure the mysql2 gem is defined in your Gemfile.
  #  gem 'mysql2'
development:
  adapter: mysql2
  encoding: utf8
  reconnect: true
  database: db/[DB name]
  pool: 5
  host: 127.0.0.1
  username: root
  password: [your password]
  socket: /tmp/mysql.sock
  port: 3306
  secure_auth: false

test:
  adapter: mysql2
  encoding: utf8
  reconnect: true
  database: db/[DB name]
  pool: 5
  host: 127.0.0.1
  username: root
  password: [your password]
  socket: /tmp/mysql.sock
  port: 3306
  secure_auth: false

production:
  adapter: mysql2
  encoding: utf8
  reconnect: true
  database: db/[DB name]
  pool: 5
  host: 127.0.0.1
  username: root
  password: [your password]
  socket: /tmp/mysql.sock
  port: 3306
  secure_auth: false