you are doing fine. you need to select ipr rendering - then select a region you want to automatically want to update. it updates automatically as soon as you change a attribute of the shader (e.g. color). if you do a before after thing to see the difference, it is good to have part of the region you want to change outside of the green area - and for performance reasons as well.

the refresh ipr image is to update the whole image without you losing the selected region that sill automatically updates afterwards.

hope that helps