You get access to core CLI via SSH. To open it you can use a Linux-SSH command line client or any other, for instance, Putty.
In production, change the username and the password to secure ones. The username can be changed in database.yml file, the password can be changes using command line.
Type help in the command line to receive information on commands.
For a detailed description of a command, you can type that command with the -h key.