Our 5 GB plan is a great place to start as it works well for most users. You can always upgrade to a higher plan, even if you've already exceeded the data in your current plan!
When you visit a web page, send email, watch a movie, etc. your device is sending and receiving data. This is the data measured for your plan. Some activities like watching videos require a large amount of data. Here are some typical online activities and the recommended data plans.