Reply: a way of participating to a discussion launched
You can participate to discussion by launching it, as already indicated in a
former post, or to react to a discussion launched by another. You react by "Reply"
Two modalities to Reply
You can reply in general to the discussion, not referring to a specific contribution of the forum member, in this case, click on "write a reply".
You can also reply to a particular contribution, in this case click on "reply" at the bottom of the related contribution.
The distinction enabled is of interest because every contributor could see what were the reactions to his specific contribution.