I noticed you put "des" as a definite article. Its not a definite article. "des" is a form of "das" and "der" in the genitive case for German, which is the possessive case. "des" would be used in a sentence, for example: Das Auto des Mannes - The man's car. In general, learning to use the definite articles correctly is one of the most difficult/frustrating things about the german language to be able to use really well, because there are so many variations that the words have to be changed to depending on the case. I would suggest that for this, you look to learning how to use them properly in an actual class with a teacher, rather than having someone try to briefly explain it to you here.

German has the most difficult grammar out of the three I think, but I find that many more of the words are similar to English than Spanish. Spanish has easier grammar but the pronunciation is harder. I've never taken French. From what I've heard a list of easiest to hardest would be Spanish, French, German. But as long as you are motivated, taking on even one of the harder languages shouldn't be super super difficult.

Many times when people say corridor, they're talking specifically about hallways in older building like in a castle or something. Think of Hogwarts in Harry Potter. That sort of setting. That's not always the case, but more often than not it is. Very few people would refer to a hallway in a modern building as a "corridor".