TL;DR: Starting a Matrix chat with another person is supported by Beeper on Android and desktop at the moment. Doing this using Beeper on iOS is still a WIP.

How to Start a Matrix DM

Using Beeper on your computer (a.k.a. Beeper Desktop) and Android, you can start DMs with other Matrix users. Though the steps are a bit different per platform, they're very straightforward.

Notes:

• Beeper is a Matrix account on its own. You can use your Beeper MXID to chat with users on other Matrix communities (:matrix.org, e.g.)

Here are the steps to create a DM chat with another Matrix user:

Desktop:

1. Click the “Start New Chat” button.
2. Type the MXID (unifiedchats:beeper.com, e.g.)
3. Click over the result, which should include their avatar, name, and MXID.

Android:

1. Press the “New Chat” button.
2. Type the MXID using this format: @unifiedchats:beeper.com (the @ is crucial).
3. Click over the result. 
   1. Heads up: Android doesn't show their name or avatar in the results.

iOS:

• Starting a new DM with a Matrix user using Beeper on iOS is still a work in progress.

FAQs

• Where is starting a new chat with a Matrix user supported?
  • Starting a new chat with a Matrix user is only supported on Beeper Android and Desktop at the moment.
• Chat Rooms (Group Chat):
  • Join a Matrix room: Joining an existing Matrix room isn't available in the Beeper desktop app at this time, but as a workaround, open your browser and visit beeper://platform-callback/hungryserv_primary/join-room/{roomID}, substituting {roomID} with the actual room ID of the Matrix room you want to join and it should allow you to join it in Beeper.
  • Add/Remove a Chat Participant to a Matrix Room (Group Chat): Open the command bar in Beeper (Mac: Command + J or Windows: CTRL + J) and type either “Add Participant” or “Remove Participant” and select that option from the menu. 
  • Leave a Matrix Room (Group Chat): Open the command bar in Beeper (Mac: Command + J or Windows: CTRL + J) and select “Leave group” to leave the chat. 
• How to report a Matrix chat as Spam?
  • Open the command bar in Beeper (Mac: Command + J or Windows: CTRL + J) and select “Report as spam”.