Learn Farsi: هر روز بیست کلمه می‌خوانم.

In Farsi, whenever you use a number (like بیست, twenty) or an asking word for quantity (like چند, how many), the noun that follows it must stay in its singular form. You do not add the plural ending ـها (-ha). So, the Farsi literally says "twenty word".

"Twenty words" is the object of the sentence. Why isn't the object marker را (ra) used here?

The object marker را is only used for definite direct objects (like "the words" or "those twenty words"). Because you are talking about reading any twenty words in general, it is an indefinite object, so را is not used.

What does the prefix می‌ (mi-) do in the verb می‌خوانم (mikhaanam)?

The prefix می‌ shows that the verb is in the present tense. It is used for both actions happening right now ("I am reading") and habitual actions ("I read"). Because of the phrase هر روز (every day) in this sentence, we know it is a regular habit.

Where is the word for "I" in this sentence?

Farsi verbs change their endings to match who is doing the action. The ـم (-am) at the very end of می‌خوانم (mikhaanam) means "I". Because this ending makes the subject obvious, the pronoun من (I) is usually dropped.