Breakdown of Strákurinn er að teikna köttinn.
vera
to be
strákurinn
the boy
kötturinn
the cat
að
to (infinitive marker)
Questions & Answers about Strákurinn er að teikna köttinn.
How does er að teikna mean "is drawing"?
This is the Icelandic way to show an action is happening right now. You use the verb vera (to be) conjugated for the subject—here it is er (is)—followed by að and the infinitive verb teikna (to draw).
Could I just say Strákurinn teiknar köttinn?
Yes, but it changes the meaning slightly. Teiknar is the simple present ("draws"), which sounds more like a general habit. Using er að teikna makes it clear that the drawing is happening at this very moment.
Both strákurinn and köttinn end in -inn. Is that the same ending?
Yes, -inn is the attached word for "the". Icelandic usually attaches "the" to the end of nouns. Since both "boy" and "cat" are masculine nouns, they both take the -inn ending in their respective forms here.
The dictionary word for "cat" is köttur. Why is it köttinn here instead of "kötturinn"?
Because the cat is the direct object receiving the action (being drawn), it must be in the accusative case. The word köttur drops its -ur ending in the accusative case, becoming just kött. Then you add -inn (the) to get köttinn.