"You write literature."
litterīs is the dative and ablative plural form. litterās is the accusative plural form.
litterās is often used as the direct object for a verb, but you have (likely) seen the use of the verb studēre which usually takes the dative like a 'direct object' instead of the accusative.
litterīs latīnīs studēo -> I study Latin literature.
litterās latīnās legō -> I read Latin literature.