At roundabouts, the traffic circulates counter-clockwise and moves toward vehicles at the yield line. Vehicle operators should always yield at the entry to circulating traffic. In practice, that means yield to traffic from the left, similar to the action that is necessary when entering a freeway or turning right at a red traffic light/signal.
A more detailed explanation and various scenarios can be found in the Iowa Department of Transportation website located here: www.iowadot.gov/traffic/roundabouts/Frequently-Asked-Questions/How-do-I-drive-in-a-roundabout#451581550-i-learned-the-rule-as-yield-to-the-right-is-that-correct-in-a-roundabout