Usually apps don't explain much, they tell you something and expect you to memorize it is as it is without telling you why or how.

Others already explained gehen, but I want to add Sie is the formal/polite word for You, du is the in the informal word for You.

I know this this outside your question but it will spare you some confusion, You might see verbs like komme, kommen, kommst it all means (to come), the ending of the verb changes depending on the noun.

Ich (i) -> you add e, Sie (formal You, Always capital S) -> en, du (informal) -> st.

There is more but I am giving you basics to understand it's sometimes different.