The speedtest measures the maximum download speed from bzzhr.co servers to your computer.

You can download a sample file used in speed test here.

How do I read these results?

If the speed is a lot slower than your usual downloads, your ISP is limiting the connection speed to bzzhr.co's servers.
To achieve better speeds, consider using download managers that support multi connections, like IDM or FDM (1DM or ADM for Android).