When you're using your iPad or other tablet on a public WiFi network, someone nearby could be eavesdropping on whatever you're doing. But iOS has built in support for Virtual Private Networks, a method of securing your traffic from outsiders who may be intercepting WiFi signals.
If you use a corporate network, check with your IT department for the proper server addresses and passwords. Many consumer ISPs also offer VPN services as part of your internet service.
To add a VPN connection to your iPad, go to Settings > General > Network > VPN. Tap the Add VPN Configuration… button. In the pane that pops up, enter the credentials for your VPN account, and tap Save when you're done.
The next time you're connecting your iPad to an open network, navigate to Settings > General > Network > VPN again, and slide the switch to On. Once your device connects, a small VPN icon will appear in the bar at the top of your iPad to let you know that you're securely connected.