"Du" is "you" as the subject of the sentence. You run. You see the dog. You eat the bread.
"Dig" is "you" as the direct object of the sentence - the thing being acted upon. The dog sees you. I thank you. The bear eats you.
"I" is a plural "you", as in "you all", and the subject of the sentence. You all run. You all see the dog.
Then there's "jer", which is plural "you" as the direct object. The dog sees you all. etc.
I wrote 'Jeg takker dig.' (copy-pasted from my answer) and it was marked wrong with a suggested correct answer of 'Jeg takker dig.'! I noticed that the (presentation) format has just changed a short while ago, while I was doing this section. Maybe this is a resultant bug? It's difficult to report with the very limited report options, none of which were appropriate. Anyone else having similar problems?