I am trying to use predecessor relationships other than "FS", and Gantter is not allowing it.  Is this not possible?   Does anyone have a list of acceptable relationships, or know how to apply them correctly?

I have tried using some of the above 4 predecessor options, and it becomes confusing.

Is there detailed help available on which task rows to select to achieve a (say) a FF relationship?

I presume the relationship always applies to the task preceding the selected task?

Or are both task rows required to be highlighted.

Is there a video on this?

I see my question has been partly answered by Matt Silva under a separate post about 5 months ago.

But, I presume the following is correct:

If a dependency is set between two tasks for which  duration/start/finish dates have already been set, then a line will be drawn between those two tasks. The type of line drawn will depend on whether FF,FS, SF or SS has been set. The tasks will remain on the chart in their original positions.

I have noticed when I have set dependencies in other situations, the task moves it's position on the chart.  Under what instances does that occur? This seems to occur when start/finish dates have also been set?

...... I see now that this probably depends on settings within Task Properties> Constraints. I presume the default constraint is ".as soon as possible".