Vertaling:I will show you what to do.
Why is "I'll show you what you need to do" wrong?
I suppose it's not wrong as such - rather a bit longer than required.
Do note that for such improvements it's best to use the 'meld een probleem'-button; e.g. see https://www.duolingo.com/comment/1386095 :)
The difference between "need to", "have to" and "must" is rather subtle in English I seem to remember. It is a subtlety we don't really have in Dutch. I think they all should be considered right. But you should just report it.
Jou laten zien means Let you see. You can let someone see something without showing them.
wy is this wrong
I will show you what you should do.