To make broadcasting message more efficient you can set some group of contacts. Either you can import from Whatsapp Group, Upload with Excel, or manually create with your own criteria on Group & Contact -> Group.
For adding new group you can click Create button on top right corner of page.
Then group form will appear, you can fill group information then click Submit to save it.
Created groups will be shown on group table, you can update by clicking Action Button -> Edit on the left for each group, or you can go to Group Detail Page by clicking their name.
For removing group you can use click Action Button -> Delete. Please remember to re-check those group before deleting.