Click the blue Compose icon in the lower-right corner
Select "Group Chat"
Choose your contacts or type in the ID number they used during account creation. Note: This is likely to be their phone number — and if they’re in your contact list, you’ll see that clearly — but it can also be a GID, or goTenna ID, a randomized string they need to share with you
Click “Create” in the upper-right corner to create group