Transitions are the final piece of your puzzle and will essentially link all your workflow components together. To set transitions, click on the transition icon on your left menu (your mouse cursor should change into a transition image). Once done, first click on the activity that starts and then click on the next item it should join to. When you're finished, your process should look like:
Essentially, we're checking for the variable name "supervisorApproval" and ensure that the value contained is "yes". For more information about workflow variables, refer to ?Workflow Variables.