Pronouns replace a noun, and like nouns they change with the case: ich (subject) → mich (direct object) → mir (receiver). Two things decide which form you need: the verb, and any preposition in front. Some verbs simply demand the dative — helfen, danken, gefallen, gehören — even though English and Persian treat them as ordinary objects. sein (to be) is the most irregular and most used verb in the language: ich bin, du bist, er/sie/es ist, wir sind, ihr seid, sie/Sie sind. It is worth over-learning, because it also builds the perfect tense of movement verbs later.
Persian verbs carry the subject in their ending — «میروم» already means I go, so the pronoun is optional. German never drops the pronoun: you must say ich gehe, never just gehe. Also watch helfen: Persian «کمکش میکنم» feels like a direct object, but German requires dative — Ich helfe IHM, not ihn.