In English, you almost never use inversion with the first person subject pronoun ("I"), unless you are using it with the past tense of a verb immediately after. You would never use this construction with a possessive adjective ("my").
Does work: "Have I found my letters?"
- This is a form of inversion with the past tense (normally "I have found"). Using a possessive adjective "my" after this construction is acceptable in English.
Does not work: "Have I my letters?"
- This is a form of inversion with the present tense (normally "I have"). Using a possessive adjective after this construction is not grammatically correct in English.
It should be noted that "Have you", or more generally present tense inversion is not very common in English. It is more correct to say "Do you have my book?" as opposed to "Have you my book?"
Colloquially, the construction Do + subject pronoun + verb (present) is the most common construction for asking questions (present tense).
- Did + subject pronoun + verb (present) = ask a question about something that happened in the past, e.g. "Did you steal my book?" (past tense).
Well, my knowledge of English grammar is based on my knowledge of French grammar, of which I was taught formally (in college; still learning!). That said, if you know the 'fancy terms' for the parts of speech (subject pronoun, for example: I, you, he, she, it, we, you, they), then you gain a bit of understanding of how languages work in general.
Tenses of verbs, parts of speech, etc. - once you learn things like that, then you can learn how they're put together (like in my example above), and with that, you'll gain a lot of insight into languages and how they work, as well as have an easier time learning them :)