I've heard many people say that in German every now in capital, is this true? I would like to know so I don't mess up when writing in German. Thanks!
If you mean every noun (typos, I know ;p), it's very true. On some phrases, not all unfortunely, you'll have Duo reminding you if you don't capitalise. I find it extremely convenient, as you see the nouns at first glance. Here is an exemple for you to see first hand https://de.wikipedia.org/wiki/Wikipedia:Hauptseite
It's not an original noun, it's a nominalization of a verb. There are some of them in German that are very common, and you can construct them from every verb. It's also possible with adjectives, mostly if you omit the noun they refer to: "Der andere Apfel ist schöner." -> "Der Andere ist schöner". "Ich finde die beiden Äpfel schön"->"Ich finde die Beiden schön".
Yes, this is true.
Actually, this fact ("In German, all nouns are capitalized.") is the first sentence of the first paragraph of the tips and notes for the very first unit of the Duolingo German course: https://www.duolingo.com/skill/de/Basics-1
I highly recommend that you read through the tips and notes for each new unit before starting to learn a new unit.
The lessons themselves can teach grammar and vocabulary only by example; there are no explanations -- but the tips+notes try to explain the most important points of grammar.
Currently, the tips+notes are only available on the website and, for a small group of test users, in the Android app.
So if you're not using the website to learn, consider switching.
Note: tips+notes may not be available on the website when viewed on a small screen (e.g. smartphone). For best results, use a laptop/PC/Mac or at least a tablet.