User toolbars, the tools and the modes for it

I am still busy with the User Toolbars. I have connected all tools to its buttons now, and reached the stage where i want to add useful descriptions to the tools. The first step here is to know how to get it to work at all. And i fail at some already because i am most obviously not in the right mode and under the right circumstances. Like for the align at edge tool.

General question, how do i see which tool can be used in what mode. Do i have to use trial and error here and go through all modes and search through the menu if my current tool is active? Or is there a hint at the tool and its description itself somewhere?

A tool belongs to a specific group and the group's name should give you the hint.

So all tools in one group are available in the same mode/s? That`s a big relief, thanks