Learn Danish: Pigen finder mange planter her. - The girl finds many plants here.

The singular word for plant is en plante, which already ends in an 'e'. When a Danish noun already ends in an 'e', you just add an -r to make it plural, rather than adding a whole extra -er.

Both finder and planter end in -er. Are they both plural words?

No, they end in similar letters but for totally different reasons! Planter (plants) is a plural noun. Finder (finds) is a verb in the present tense. In Danish, present tense verbs almost always end in -r or -er, regardless of whether the subject is singular or plural.

Why does pigen end in -n while planter ends in -r?

These endings do different jobs. Adding -n or -en to a singular noun makes it a specific thing, so en pige (a girl) becomes pigen (the girl). Adding -r or -er makes a noun plural, so en plante becomes planter (plants).

Do I always use mange with plural words like planter?

Yes, mange translates to many and is used with things you can count, which are plural nouns. If you want to talk about uncountable things like water or time, you use the word meget instead.