Admin > Comms.
On the left hand side of this page you will see a "Student Search" dropdown. Use this to find the students you wish to create a group for.
Once you have chosen all the students and they are shown on the page with their details, click the green button that says "Save Group".
Choose a name for the group and click save. If you have have groups saved in Comms already, you will also get the option to add these student to an existing group.
Click "Staff" above the student search and repeat these steps to create a staff comms group.