Learn Icelandic: Hún gefur manninum stundum heftarann. - She sometimes gives the man the stapler.

The verb gefa (to give) is a ditransitive verb, meaning it takes two objects. In Icelandic, the recipient or indirect object (manninum) takes the dative case, while the thing being given or the direct object (heftarann) takes the accusative case.

Is it normal to put the adverb stundum right in the middle of the two objects?

Yes, adverb placement in Icelandic can be quite flexible. While adverbs like stundum (sometimes) often go right after the verb (Hún gefur stundum...), putting it between the indirect and direct objects is also completely natural and common. You could even put it at the very beginning of the sentence.

How do we get from the dictionary word for man (maður) to manninum?

The word maður is highly irregular. Its stem changes to mann- in all other cases. Because the verb gefa requires the dative case for the recipient, we use the dative singular form manni, and then add the dative masculine definite article -num to get manninum (the man).

Why does the word for stapler end in -ann here?

The base dictionary word is heftari, which is a masculine weak noun. In the accusative case, it becomes heftara. To say the stapler, we attach the masculine accusative definite suffix -nn, giving us heftarann.