fan running

Click on this link to read about fans and fan noise in your Apple product --> About fans and fan noise in your Apple product - Apple Support

See this document about the operating temperature of Mac notebooks - Keep your Mac laptop within acceptable operating temperatures - Apple Support

If your Air has a fan your Mac automatically controls the fan speed depending on internal temperatures. So if it determines it needs more air flow for cooling it will speed up the fan then lower it when temps reach closer to normal values. It’s all automatic so nothing to be concerned about.