Welcome to Android Central! Do you have a data plan through your carrier (i.e., 3G/4G data)? If so, go to
Settings>More Networks>Mobile Networks, then make sure Mobile Data is checked on. To make this easier, you can install a mobile data toggle widget from Google Play Store, which you place on your homescreen, and which you can tap to turn mobile data on or off more easily. I like
Power Toggles.
If you have access to a wi-fi network, you can also turn on wi-fi. Go to
Settings>Wi-fi, and turn it on, then tap on the network you want to connect to.