Questions & Answers about Hann skellti bókinni á borðið.
Skellti is the 3rd person singular past tense of the verb skella.
So in this sentence it means that he did the action, and that the action happened in the past. The dictionary form is skella.
A useful thing to notice is the ending -ti, which is a common past-tense marker in some Icelandic weak verbs.
Because the verb skella takes its object in the dative in this kind of sentence.
English speakers often expect the direct object to be like an accusative object, but Icelandic does not always work that way. Some verbs simply require a different case, and skella is one of them here.
So:
- bókinni = dative singular definite
- not bókina = accusative singular definite
This is something you often have to learn with the verb.