Click on the System Preferences icon in the dock. (If you don't have System Preferences in the dock, then it's probably in your Applications directory). Then, click on the "Network" icon in the "Internet & Network" section of the System Preferences. This will bring up the network panel.
If you are currently connected to the internet using an Ethernet cable, the colored dot next to "Built-in Ethernet" should be green. If you are connected to the internet wirelessly, the colored dot next to "Airport" should be green.