Association worker refresh ?

This is my first time playing and I’m confused about the association workers. (Currently in a two player game)

It lets you start with one “active” worker on the notepad. And the other three are laying flat and my understanding is they are locked until you meet the conditions to hire more.

But when you put one worker on an association spot does it stay there? What if I want to do another association action? Then I don’t have any more on the active space to use? What am I missing here