To run docker commands, you either need to be a root user or run the commands with sudo.
To run docker commands with a regular user, you need to add that user to the docker group.
The docker group manage the access to the dockerd Unix socket.

By default the group docker is created.
$ grep docker /etc/group docker:x:999:

• Add a user to the docker group:
  $ sudo usermod -aG docker mtitek
  
• You need to log out and log in to your account to activate the changes to groups.
  You can optionally use the command newgrp to activate the changes to groups during your login session:
  $ newgrp docker
  
• Verify that you can execute docker commands with your user:
  $ docker run hello-world Hello from Docker! This message shows that your installation appears to be working correctly.