The Single Value column lets you display the same value for every row in a table. The source of that value can be from any other table, from a Multiple Relation or Query in the same table, or from an Array in the same table.
In the Data Editor, open the table you want to edit.
Add a new column by clicking the plus (+) symbol to the right of the table.
New columns added with the plus button will always appear on the right. If you'd like to add a column somewhere else in your data, you can select the dropdown menu on an existing column and choose Add column right. You can also click and drag columns to rearrange them.
Give the column a name.
For Type, search for Single Value or navigate to Computed → Single Value.
Under Configuration, the first dropdown Get allows you to choose where in that table the single value will be retrieved. You have the options of:
First: get the first or topmost value from the source
Last: get the last or end value from the source
Random: get a random value from the source
From start: get a value X number of places from the start of the source
From end: get a value X number of places from the end of the source
The second Configuration value From allows you to choose the column from your tables from which to retrieve the value.
The Single Value column can also bring back a Whole Row as opposed to just a single value. You can choose the Whole Row option in the From dropdown while setting up the row. This allows it to behave similar to a Relation Column. It can also be used as a form of Navigation by adding the Show New Screen or Show Detail Screen actions to the Component or Collection item that displays the value in the Single Value column.