Learn Swedish: Han läser meddelandena. - He is reading the messages.

The base word is an ett word ending in a vowel: ett meddelande (a message). First, we make it plural by adding -n, which gives us meddelanden (messages). Then, to make it definite ("the messages"), we add -a to the plural form, resulting in meddelandena.

Why does meddelandena add an -a instead of the -na ending seen on other words?

The definite plural ending depends on the word group. For ett words that end in a vowel, the definite plural suffix is just -a. Since the plural form meddelanden already ends in an n, adding -a creates that familiar -na ending sound naturally.

Why is läser translated as "is reading" instead of "reads"?

Swedish does not have a separate continuous tense like English does. The present tense verb läser can mean either "reads" as a daily habit or "is reading" right in this moment. The context of the situation tells you which one is meant.