You can set your forum name on your profile page. Until you do this, we will use a temporary name, such as NAS12345. Your forum name should not obviously relate to your real identity, and therefore is different from the username that you created for signing in.
Finding your profile page
First, make sure that you are signed in. Then, go to your profile, by clicking on your "avatar" at the top of the screen. Next, click on Profile in the drop-down panel. On a desktop or laptop, the avatar should be in the centre:
Finding the avatar on a mobile device
On a mobile device, open the "hamburger menu":
Touch the avatar to drop down the menu giving access to your forum profile:
Editing your profile and avatar (on desktops and mobiles)
Then click Edit Profile, and you can type a new name into the box at the top of this screenshot, and also change your avatar to one of your choosing:
Make any other changes that you wish, such as to your biography text, and then click Save Profile. Other forum users can see this profile by clicking on your username in any post that you make, so it is a good place to give a little background about yourself. Again, however, you should not include information that would allow you to be identified.