To start a discussion:

Go to your Project.
Click on Start a Discussion option under the More option on right.

ALTERNATELY

From the main menu, click on Add > Discussion. Select the project where the discussion should be created.

In the Summary box, type the Discussion name.
In the Detail box, type comments.
You can add users to follow the discussion. The followed users will receive an email notification.
Select the Share with client check box, if you want it to make it visible to the client.
Click Save. The topic is created.

If your company policy Auto subscribe team members to new discussion topics, is selected the all the members of the project team are subscribed to the discussion automatically and will receive a notification.

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