The Edit Properties dialog is used to select a tag to be written to and the value to write to it.

Use the tag browser button,
to select a tag to be written to.
Its name will be shown in the Tag field.
The Value to be written may be a constant (0, 1, etc.) or an expression. You may also select another tag to provide the value. If the value to be written is not a constant, then the current value of the associated tag or expression at the moment that the MultiWrite is triggered will be written.