Chat commands allow user to perform common operations on GitLab right from there chat client. Right now both Mattermost and Slack are supported.
The trigger is configurable, but for the sake of this example, we'll use /trigger
/trigger help - Displays all available commands for this user/trigger issue new <title> <shift+return> <description> - creates a new issue on the project/trigger issue show <id> - Shows the issue with the given ID, if you've got access/trigger issue search <query> - Shows a maximum of 5 items matching the query/trigger deploy <from> to <to> - Deploy from an environment to another