Translation:With this you can see stars and dreams.
Well, loosely, it's "with", but that doesn't mean it can be used interchangeably with "met". It can be part of a separable verb, e.g. meezingen (to sing along): https://www.duolingo.com/comment/5585385.
Duolingo also has it in this example: https://www.duolingo.com/comment/9656524
"To take someone along" (i.e. on a trip). I'm not absolutely sure, in the latter example, whether it's a word in its own right, or it's actually another separable verb: meenemen.
Note that when it's used in the "along" sense, it's still always in the sense of: "with". You can't use it to say: "along the corridor".
"With this", "with that", "take along (with)", "sing along (with)"...
"Herewith" is a little bit old-fashioned. You might still see it in formal correspondence (especially legal) - usually referring to something that is attached/included. E.g. "I enclose herewith the deed for your signature." That means you should expect to find the deed (a type of formal legal document) in the same envelope.
Nobody ever uses "herewith" in normal conversation, and I'm not sure you would even find it in rather old textbooks, as I think the meaning is always: "accompanying this", rather than what you can or should do with something.
I use it in everyday speech, but I'm weird. And I'm a lawyer. It's just so handy (also whereby, therefor, herein, whereto). And familiarity with those words appears to give me a bit of a leg up on Dutch.
But yes, they are a bit old-fashioned and, these days, formal-sounding. I blame William the Conqueror.
Although "hiermee" can be translated as "with this", it can also be translated as "with these".
In other words, "hiermee" can refer to multiple objects, not just a single object.
And that is true in general of the Dutch pronomial adverbs. Instead of pronouns that are clearly either singular or plural, the pronomial adverbs use an adverb that no longer delimits number.
Therefore, Duo should also accept "with these" as well as "with this" as a translation here. Reported.