Learn Swedish: Jag skrev ett brev om Annas liv. - I wrote a letter about Anna's life.

Skriva (to write) is a Group 4 strong verb. Instead of adding a regular past tense ending like -de or -te, these verbs change their root vowel in the past tense. Here, the i changes to an e, making it skrev without any extra suffix.

Is there a typo in Annas? Shouldn't it have an apostrophe like in English?

There is no typo! In Swedish, you show possession simply by adding an -s directly to the end of the noun or name. You never use an apostrophe for this in Swedish, so Anna's becomes Annas.

Does the word om always mean about?

Not always. In this sentence it translates to about, but om is a very common and flexible word. It is also the Swedish word for if, and it is used to mean in when talking about future time, such as om ett år (in a year).

How would I say Anna's lives if I wanted to make liv plural?

You would still just say Annas liv. The word liv is an ett-word that ends in a consonant (ett liv). These types of nouns do not change form in the plural, so liv can mean life or lives depending entirely on the context.