Selecting a specialism makes it easier to help engineers in your field when they ask questions. Unanswered questions in your specialism are displayed in the 'can you help' section of the home page.
You can edit your specialisms by visiting your profile. Find your profile avatar in the top right corner and select profile in the drop-down menu. On your profile page, select edit and scroll down until you see the available specialisms. You must have already selected your specialism as an interest for it to display as an available specialism.