Bonus Bytes is the data that is used between 2AM and 8AM. Anytime Data is used between 8AM and 2AM, unless you run out of Bonus Bytes, in which case your Anytime Data will be used during the 2AM to 8AM time period, as well, hence the name "Anytime Data". It doesn't work the opposite way, though, as Bonus Bytes are ONLY used during the 2AM to 8AM period, even if you've run out of your Anytime Data.
Anytime you do something online it uses data.
Also, though most of the data you use will be of the "download" type, both download and upload data are counted.
Hope this helps.