The Speed Check measures Ping, Upload Speed, and Download Speed. This should, over time, match pretty closely with the plan speed that you get from your ISP. You'll see the results of your Speed Checks plotted on a graph under the Internet Speed section.
If you're not getting the speed you pay for, you might want to contact your ISP to let them know. You can run Speed Checks on your Starry Station or from the Starry App for iOS (we're working on adding this feature to the Android App). You must be connected to the Starry Station Wi-Fi Network to run a Speed Check.