You can find your profile page by hovering over your avatar in the top navigation bar, and clicking "view profile".
There are two parts to a profile, the top part is your global profile, this will show on all wikis. The bottom part is your user page, this can be different for each wiki you use.
To edit your global profile, hover over the profile box and click "edit". This will take you to a form where you can add information about yourself. Any section you leave blank won't show on your global profile.
To edit your local profile, go to the wiki where you want to add information and click "edit profile". This works the same way that editing articles on a wiki does - you can add text, images, and anything else you want to show.
For more, see our help page on profiles.