Breakdown of Du lernst schnell, danke.
du
you (informal singular)
lernen
to learn
schnell
fast, quickly
danke
thank you
Questions & Answers about Du lernst schnell, danke.
Why does the verb end in -st here (lernst)?
Because the subject is du (the informal "you"). In German, when you use du, the verb drops its standard -en ending and takes -st instead. If you were being formal, you would say Sie lernen.
Who would I say this sentence to?
Because it uses du, you would say this to a friend, a family member, a child, or a peer in a casual setting. If you were praising an adult stranger or someone you have a professional relationship with, you would use the formal version: Sie lernen schnell, danke.
Does the word schnell mean "fast" or "quickly"?
It means both! In English, we often add "-ly" to turn an adjective into an adverb (quick vs. quickly). In German, the exact same word is used for both. So schnell is used to describe a fast car, as well as how quickly someone learns.
Is danke a verb that changes depending on who I talk to?
No, in everyday speech, danke acts as a fixed word for "thanks" or "thank you". Even though it is related to the verb danken (to thank), this specific greeting does not change whether you are speaking informally to a du or formally to a Sie.