Translation:Are you spying on us?
Have another look at the Tips and Notes for the "Vocab. 1" unit -- those list most of the verb subject/object prefixes. A few more are in the "Aspect" unit Tips and Notes, and some of the most common ones (e.g. vI-) are in earlier units.
We've tried to cover all the grammar in the Tips and Notes so that people won't have to keep asking questions scattered over the various sentence discussions; if there is anything unclear, missing, or contradictory in them, please do let us know.
If you haven't found the Tips and Notes yet -- when on the website https://www.duolingo.com/ , then after clicking on a unit you will get a little window open that has a Start button, a key, and a lightbulb; click on the lightbulb to access the Tips and Notes:
If you're using a mobile app to learn, you probably won't have access to the Tips and Notes in the app, making the app not very suitable to learning languages on Duolingo. (They can be useful for repeating material you have already read the notes for on the website.)