It is important to set expectations with your clients in as many ways as you can - it is a principle that is deeply engrained in Sprout Studio in a variety of ways.
When your client first views their gallery, you can optionally include a Welcome Message to greet them. For example, you may want to remind them what they have included in their collection, give them instructions on how to download their images, tell them about the expiry date of the gallery, and so on.
By default, there is no welcome message in a gallery, so nothing will be displayed. To add a welcome message to a gallery:
Click the "X" button next to the "No Message" card in the "Message Template" panel while editing a gallery.
Create a new message or choose a message template from the list of message templates. To create new message templates, go to Settings > Galleries & Albums > Online Galleries > Online Gallery Messages to create, edit and manage your message templates.