Learn Icelandic: Þetta er hundur og hann er þar.

In Icelandic, nouns have a grammatical gender: masculine, feminine, or neuter. The word for dog, hundur, is masculine. When you refer back to a masculine noun, you must use the masculine pronoun hann (he), even if it translates to "it" in English.

Both halves of the sentence use the word er. Why is it the same?

The verb vera (to be) is irregular, but it shares the same form for all third-person singular subjects. Since Þetta (this) and hann (he/it) are both third-person, they both use the form er (is).

Does Icelandic have a word for "a" or "an" like in "a dog"?

No, Icelandic does not have indefinite articles. The word hundur means both "dog" and "a dog" depending on the context. In Icelandic, you literally say "This is dog".

Why do we use Þetta at the beginning of the sentence?

Þetta is a pronoun used to point things out, meaning "this". When introducing or pointing to something for the first time, Icelandic typically uses this neuter form Þetta, regardless of whether the noun that comes after it is masculine, feminine, or neuter.