You can send private messages to other people or groups of people in the forum.
To send a private message you need to go to the person’s profile. You can do this by clicking on their name in the forum. Clicking on their icon will only show you their activity. You can also see all users by clicking the forum menu at the top and selecting members.
At the top right of their profile, you will see an envelope. just click this to send a private message.
To view your private messages goto your own profile, click on your name in the forum or use the forum menu at the top and select edit profile.
Select the message tab and use the hamburger on the left to switch to other users.