Bilde den Plural folgender Substantive: Kuh, Regal, Schuh, Erdbeere, Haus, Maschine

This question asks you to build the plural form of some nouns.  Some of them follow the regular pattern for building the plural: adding an "e" at the end of the word, or an "n" if the word already ends on an "e". Others might be slightly irregular and you need to memorise them. One important thing to remember is that some of them undergo vowel mutation. 
I would suggest that you try building the plural first, and we then go through your answers together to see what isn't clear yet.