You can create DMs by clicking on the chat icon below at the top right.
selecting this will open the chat window below:
Alternatively, you can access DMs from the left hand navigation
Chat toggle
The toggle toolbar allows you to attach a file, insert date/time and insert a template.
Individual chat
Chats can be with an individual or group
Group chat
You can name the group chat, each member of the group chat will be listed in the member window.
Chat window
Opening chat will display the Chat Window.
By default, messages in channels last for 90 days