Ok. Simply add a chart object to your model (found under the tab User Interface) and drag the machines you want to look at onto the chart object. You'll get a prompt asking what you want to observe, select "Resource Statistics". Then you'll get a handy graph like this one
You can then open the chart object and goto the Data tab --> Input Channels to add/remove stats that you are missing/ are not intereseted in.
I think, it is generally a good idea to insert a chart and use the Statistics Wizard.
Insert Chart > Right Click on icon > Statistics Wizard
There you can see which part of the value chain is blocked the most. As a general rule, the bottleneck is the successor of the most blocked station.