You can add a text above your gallery or question page in different ways.
If you are working on a gallery (vote campaign):
Go to the "Votes" step of your campaign, in the section "Optional text above the gallery", and enter your text:
If you add an introduction above the gallery, it will ONLY appear in the global view of the gallery (not in the zoom mode).
If you are working on an upload campaign:
You will find this option in the "Settings" step:
If you are working on another type of campaign:
Go to the "Questions" step, in the "Optional introduction text" section, and enter your text:
If you add an introduction text in a campaign with one question per page, it will appear above each question.
If you add an introduction text in a campaign with all questions displayed on the same page, it will appear at the top of the screen.