من یک سیب میخواهم.

من means I and makes the subject explicit: I want…. In Persian you can omit من because the verb ending often already implies the subject.

• من یک سیب می‌خواهم. = I want an apple. (explicit)
• یک سیب می‌خواهم. = (I) want an apple. (very common in conversation)

یک literally means one, but very often it functions like the English indefinite article a/an. So یک سیب can mean an apple (not necessarily emphasizing “one”). If you stress یک, it can imply one (not two).

Not always. You can say:

• سیب می‌خواهم. = I want apple / I want some apple / I want an apple (context decides)
• یک سیب می‌خواهم. = I want an apple / one apple (more specific)
  Using یک often makes it clearer that you mean a single item.

The correct standard spelling uses a half-space (ZWNJ) between می and the verb: می‌خواهم. In casual typing people often write it without the half-space: میخواهم. Both are understood, but می‌خواهم is more correct and readable.

می‌ is a prefix that usually marks the imperfective/present form (often translated as I want / I am wanting / I would like depending on context).
Here, خواستن = “to want,” and می‌خواهم = “I want.”

The ending tells you. The verb is built like this:

• می‌خواه- (verb stem) + -م (ending for I)
  So می‌خواهم = I want.
  (For comparison: می‌خواهد = he/she wants.)

Persian is flexible, but the most neutral order is what you have:
من یک سیب می‌خواهم. (Subject + Object + Verb)
You can move من or the object for emphasis:

• یک سیب می‌خواهم (من). = I want an apple (as for me)
• من می‌خواهم یک سیب. is less natural; the verb usually comes at the end in normal statements.

Usually no in this sentence. را marks a definite/specific direct object. With یک سیب (indefinite), را is typically omitted.
You might see را if the apple is specific in context, but it can sound marked:

• من یک سیب می‌خواهم. = I want an apple. (normal)
• من سیب را می‌خواهم. = I want the apple (that one). (definite)

Literally it’s I want an apple, but in everyday Persian it can also function like I’d like an apple depending on tone and situation. For extra politeness, Persian often uses other constructions, for example adding politeness markers or different verbs (learners commonly encounter forms like می‌خواستم… or adding لطفاً in requests). The base sentence is neutral and commonly used.

Because یک is singular, سیب stays singular. For plural you’d use سیب‌ها (apples):

• من سیب می‌خواهم. = I want (some) apple / apples (context)
• من سیب‌ها می‌خواهم. = I want the apples / apples (more explicitly plural, often more definite)
• من چند تا سیب می‌خواهم. = I want a few apples.

A common pronunciation (informal speech) is roughly:
man yek sib mikhâham
Notes:

• خ is like a throaty kh sound.
• می‌خواهم is often said quickly; vowels can reduce in fast speech.
• Stress is usually light; don’t over-stress یک unless you mean “one.”

Persian doesn’t have grammatical gender like Spanish/French. سیب has no masculine/feminine form, and adjectives don’t change for gender. So you don’t need agreement rules like a red apple vs gendered forms—adjectives stay the same:

• یک سیب قرمز می‌خواهم. = I want a red apple.