The Block is the area of the page reserved to textual content, i.e. the gallery description. You may use Markdown syntax to format text in this area, allowing you to insert hyperlinks, lists, inline images, etc.
Taking a closer look at the controls …
The block may be positioned either above the grid (the image gallery or media area), below the grid, or removed altogether. Your content may be aligned left, right or center.
You may insert an image from your filmstrip into the block content, large and center, or to the left or right of your text. The image ID is the numerical position of the image in your filmstrip (an image ID of 1 will insert the first image in the filmstrip). You will also find controls here to adjust padding and border on your image.
The block also has the usual block-element control set for setting width, background-color, borders, etc. so that you may box your content if you'd like.
Finally, this checkbox deserves an explanation:
This controls the visibility of block content on mobile and other small-display devices. When enabled, content will be collapsed by default. Collapsed content may be made visible by pressing the content button in the mobile view. If disabled, content will be visible by default on mobile devices. In general, follow these guidelines:
When managing image galleries via TTG CE3 Publisher, what you enter into the block in the Web module is irrelevant. For publisher galleries, the block content will be set for each album from Publish Services when creating the gallery. Therefore, when creating publisher templates, you may leave the block blank or keep the default content.
However, if you wish the block to be apart of your template and to use it from the Publisher, the block must be enabled – either Above or Below the grid – during template creation. If the block is disabled, it will never appear in published galleries.