You can change your status for others to see and set status messages. 

Set your status message in Teams:

1) Tap your profile picture in Teams to bring up a menu

2) Select Set status message

3) Type your status message. You can choose to @mention people specifically, choose to Show when people message me, and if you want it to Clear after a certain period of time or never clear.

Tip:  If you prefer not to be disturbed, you can check Show when people message me and your status message will display above their message to let people know you're unavailable.

Change your status in Teams:

1)  Tap your profile picture in Teams to bring up a menu 

2) Tap your current status and select what you want to update to:

 - Available

 - Busy

 - Do not disturb

 - Be right back

 - Away

 - Appear offline

 - Reset status