Learn Icelandic: Settu bílinn í gír og stígðu á kúplinguna. - Put the car in gear and step on the clutch.

Settu comes from the verb setja (to put). In commands, you take the imperative form set and attach the pronoun þú (you) to the end. Because set ends in a voiceless 't' sound, the þ in þú turns into a hard 't', giving us the suffix -tu. So, set + þú becomes settu.

Why does stígðu (step) take a -ðu ending instead of the -tu ending seen in settu?

The suffix changes based on the sound right before it. The imperative form of stíga is stíg. Since it ends in a voiced sound (the 'g'), the attached þú softens into -ðu. The rule of thumb is: use -tu after voiceless consonants, -du after l, m, n, and -ðu after vowels and voiced consonants.

Both í gír and á kúplinguna use prepositions. Why are gír and kúplinguna in the accusative case rather than the dative?