Learn Finnish: Tehdään nuotio tänne! - Let's make a campfire here!

Tehdään is the passive present form of the verb tehdä (to do / to make). While it literally means "is done" or "is made", spoken Finnish uses this exact passive form for "we" sentences. When you use it on its own without the pronoun me (we), it becomes a suggestion or command meaning "Let's do" or "Let's make".

Why is the object nuotio in its basic dictionary form, rather than nuotion?

In Finnish, the object of a passive verb drops the -n ending. Because "Let's" commands like tehdään are grammatically passive, their total objects always take the basic nominative form. If you said "I make a campfire" (active), it would be Minä teen nuotion, but for "Let's make", the object is just nuotio.

Why use the directional word tänne (to here) instead of the static täällä (at here)?

Finnish focuses strongly on the direction of an action. When you make, build, or put something somewhere, Finnish views the result as arriving to that location. Because you are establishing the campfire into this spot, you have to use the directional tänne.