"im" is the contraction of "in+dem" right?? what is "dem"? According to the explanation it means "the" but I though "the" was translated as "der, die, den or das" but not as "dem".
It is a dative of masculine definite article. Der is nominative, dem is dative, den is accusative. The other words you mentioned are nominatives of other genders' definite articles: die is feminine and das is neuter.
@ novice, i guess im can mean both "in the" and "at the". I wrote, Are you in the restaurant?, and got it right but were also given the other option :)
why not " are you in restaurant? " they never say Das Restaurant to make me use "the" ??
Because there is a definite article present (im = in dem, dem is a definite article) and you have to translate it as a part of the sentence (meaning you have to use “the” in the English translation).
Technically you are right, but German unfortunately doesn’t work that way: Even though the person in obvious from the verb form, you have to state the subject. (Just an interesting fact: Slavic languages usually don’t require subject to be explicitly stated. The verb form alone is sufficient. German is not a Slavic language though. :)