Learn Finnish: Kävelkää opettajan perässä!

Kävellä (to walk) is a type 3 verb. To form the plural or formal command, you take the basic form, drop the final -lä to get the stem kävel-, and add the plural command ending. Because of vowel harmony (the word contains ä and e), we use -kää instead of -kaa, giving us kävelkää.

Why is the word for teacher (opettaja) in the genitive form opettajan?

It goes with the word perässä (behind). Perässä is a postposition, which works like an English preposition but comes after the noun. In Finnish, most postpositions require the word right before them to take the genitive -n ending.

Does the word perässä have a more literal meaning?

Yes! It is built from the noun perä, which means the back or rear. It has the ending -ssä (in), so it literally means in the rear. When used as a postposition, it translates naturally to behind or following.

Why isn't the word for you plural (te) included in this sentence?

In Finnish, when you are giving a command, you usually drop the pronoun te (you, plural or formal). The -kää ending on kävelkää already tells us exactly who is being told to walk, so the pronoun is not needed.