To create a group chat, tap dialogue+ icon in the top right corner of the Chats page and select which friends you want to join the group. Tap the blue 'Chat' button that appears below.
Once the group is created, you can edit the name, add more people, share the group invite link, and manage group notifications inside the Group Info page. Group Info is accessible by tapping on the header of the open chat.
The other way to create a group chat is to open an existing chat with one person. First, tap icon in the top right corner of the chat. Then, tap the settings icon in the top right corner and add anyone else to your existing chat. You can also add more people to existing groups by doing the same thing.
Happy group chatting!