If you want conditional logic, I would go straight to using scripting. (You can do some things using simple commands and @modifiers but it's easier to do it with scripting, especially if you end up needing anything complicated later.)
function OnClick(clickData)
{
var cmd = clickData.func.command;
if (clickData.func.sourcetab.selected.count == 0)
{
cmd.RunCommand('CreateFolder READAUTO=no');
}
else
{
cmd.RunCommand('Help ABOUT');
}
}
selected tells you if any files or folders are selected. There are also variants for just files or folders. The Opus Manual menu at the top-right of the forum has quick links to the scripting objects and an introduction, while the Forum Help menu has info on creating a new script button.
When a new script button is made, you'll also be given a stock example script which demonstrates lots of things.