Learn Icelandic: Við lesum bréf.

This lesson introduces the accusative case (used for direct objects), which often changes the endings of nouns. However, bréf is a neuter noun. In Icelandic, neuter nouns are completely immune to changes in the accusative case—they always look exactly the same as their basic dictionary form!

Where is the word for "a" in Við lesum bréf?

Icelandic doesn't have an indefinite article (the words "a" or "an" in English). Because of this, a bare, unattached noun like bréf automatically translates to "a letter" when it makes sense in English.

Why does the verb lesum end in -um?

Verbs in Icelandic change their endings based on who is doing the action. The -um ending is the standard present-tense match for við (we). Any time you say "we do something," the verb will almost certainly end in -um.

Can bréf also mean a letter of the alphabet (like A, B, C)?

No, bréf only means a written message you send to someone (like mail). If you want to talk about a letter of the alphabet, you would use the word stafur instead.