You totally can. Technically sometimes you need a certain conjugation or a linking "s", but usually you just combine the words. I guess they meant that not eve

You totally can. Technically sometimes you need a certain conjugation or a linking "s", but usually you just combine the words. I guess they meant that not every compound word is one that Germans actually use (as you would expect when somebody claims "it's a German word"). But you can totally make up words on the spot that every German will understand