"It is a menu."
Translation:Det er en menu.
If an unspecified IT is the subject of the sentence-performing the action-it'll always be the default DET. "It is rainy," "It [I don't know what though] is smoking."
On the other hand, if I know what I'm talking about, I'll use the appropriate form. So for "The book is..." it'll be "Den [bogen] er...."
And of course when IT is an object ("She eats it") we'll use the form appropriate to the item
I notice that in the tips and notes it says that 'it' can be den or det. I had assumed that the choice would depend on the gender of the objects, but i must be wrong, as here we have 'en menu' and we're using 'det'. The same happen with 'en bog'. Can someone explain why/when we should use 'den/det' for it?
I think here it's because "it" at first isn't defined until you say that "it" is a menu or a book or a tree and so on. A sentence or clause after this might then go something like this Det er en menu og den er på dansk. meaning "It is a menu and it is in Danish" (not the best example, I know, but my brain isn't quite with it today).
It is dependent on the gender. Et barn, en sandwich, et hus, en bog. There's no logic really to the gendering of words, you need to learn each individually :) rule of thumb is that if you forget the gender for the word, there are more 'en' words in Danish so better to go for 'en'!
There are two grammatical genders in Danish: common and neuter. All nouns are mostly arbitrarily divided into these two classes. The singular indefinite article (a/an in English) is en for common nouns and et for neuter nouns. They are often informally called n-words and t-words.
En dreng. A boy.
Et fængsel. A jail.
Hope this can help :)