How do I see who’s online in the Discord server?

To see who is online on Discord:

Open the Discord app on your device.
Click on the server or channel where you want to see who is online.
In the list of users on the right-hand side of the screen, you will see the online status of each user.
You can also left-click on a user's name to see more detailed information about their online status, such as whether they are in a voice channel or using Discord on a different device.

A green dot next to their name indicates that they are online and available,
A yellow dot indicates that they are idle,
A red dot indicates that they are set to “Do Not Disturb” which prevents a notification sound from playing when messages are sent to them or in a channel they are apart of.
A grey dot means they are offline.