I just started learning JMeter today. Wrote a simple web test - 10 user, 1 iteration to hit a webpage, but in the "view result tree" I get "JMeter Response code: Non HTTP response code: java.net.UnknownHostException"
Most probably you're behind a corporate proxy, your computer is not connected directly to the Internet, it is connected via special machine which grants Internet access to other computers over the network.
You need to make JMeter aware of this proxy, it can be specified at
"Advanced" tab of the HTTP Request sampler (or even better HTTP Request Defaults)
Via command-line arguments like:
jmeter -H your-proxy-host -P your-proxy-port
Via system.properties file like:
https.proxyHost=your-proxy-host
https.proxyPort=your-proxy-port
More information: Using JMeter behind a proxy