The following rules show the different ways that German nouns form the plural. All plural nouns in German have the article "die" in the nominative case. While these rules may help you to predict how a specific noun forms its plural, learning noun plurals is a lot like learning gender. So it is best to simply learn a noun together with both its gender and plural form.

1) no ending (the stem vowel may change to an "Umlaut" form)
der Teller - die Teller (no vowel change)
der Garten - die Gärten
See column 1

2) ending "-e" (the stem vowel may change to an "Umlaut" form)
der Tisch - die Tische (no vowel change)
der Plan - die Pläne
See column 1

3) ending "-er" (the stem vowels a, o, u and au may change to an "Umlaut" form)
das Kind - die Kinder (no vowel change)
das Dach - die Dächer
das Loch - die Löcher
das Buch - die Bücher
das Kraut - die Kräuter
See column 1 and 2

4) ending "-en", "-n" or "-nen" (no vowel change)
die Frau - die Frauen
die Kugel - die Kugeln
die Rentnerin - die Rentnerinnen
See column 3

5) ending "-s" (no vowel change)
das Auto - die Autos
See column 3