Learn Icelandic: Set stólinn þangað og bros! - Put the chair there and smile!

To give a command to one person, you use the root stem of the verb. For a verb like brosa (to smile), you drop the infinitive ending -a to get bros. For setja (to put), you drop the -ja to get set.

I usually see commands ending in -tu or -ðu. Why aren't we using settu and brostu?

Both forms are correct! In everyday spoken Icelandic, it is very common to attach the word for 'you' (þú) to the end of the command, creating forms like settu and brostu. The shorter stem forms used in this sentence (set and bros) are perfectly valid but can sound a bit more formal, abrupt, or poetic.

Why does the word for chair lose an L, becoming stólinn instead of stóllinn?

The dictionary form for chair is stóll, which is a masculine noun. Because you are doing something to the chair (putting it), it becomes the direct object and takes the accusative case form, which drops one L to become stól. When you attach the word for 'the' (-inn), you get stólinn.

I learned that 'there' is þar. Why does this sentence use þangað?