Quiero mandar un mensaje a mi amiga.

In Spanish, subject pronouns are often omitted because the verb ending already shows who the subject is.

• quiero = I want
• The -o ending tells you it is yo.

So:

• Quiero mandar un mensaje... = perfectly natural
• Yo quiero mandar un mensaje... = also correct, but yo is usually only added for emphasis, contrast, or clarity

For example:

• Yo quiero mandar un mensaje, pero ella no.
  = I want to send a message, but she doesn’t.

Yes, both mandar and enviar can mean to send.

In this sentence:

• mandar un mensaje is very natural and common
• enviar un mensaje is also correct

A rough difference:

• mandar often sounds more everyday and conversational
• enviar can sound a little more neutral or slightly more formal, depending on context

In Spain, mandar un mensaje is very common.

So all of these work:

• Quiero mandar un mensaje a mi amiga.
• Quiero enviar un mensaje a mi amiga.

Spanish often uses an article where English also would.

• un mensaje = a message

Without un, the sentence would sound incomplete in normal Spanish, because mensaje is a countable noun here and needs a determiner.

So:

• Quiero mandar un mensaje... = correct
• Quiero mandar mensaje... = not natural in this context

Here, a means to.

The structure is:

• mandar algo a alguien = to send something to someone

So:

• un mensaje = the thing being sent
• a mi amiga = the person receiving it

This a is part of the normal pattern of the verb:

• mandar una carta a alguien
• enviar un correo a alguien
• dar un regalo a alguien

So in this sentence, a mi amiga means to my friend.

Because mi without an accent is the possessive adjective meaning my.

• mi amiga = my friend

mí with an accent is a pronoun meaning me, usually used after a preposition:

• para mí = for me
• a mí = to me

So:

• mi amiga = correct
• mí amiga = incorrect

Because amiga refers to a female friend.

• amigo = male friend
• amiga = female friend

Since the sentence says mi amiga, the speaker is talking about a female friend.

Also notice that mi does not change for masculine or feminine in the singular:

• mi amigo
• mi amiga

Yes, absolutely. That is very natural Spanish.

• le = to her / to him
• mandarle = to send to her/him

So these are both correct:

• Quiero mandar un mensaje a mi amiga.
• Quiero mandarle un mensaje a mi amiga.

The second version includes the indirect object pronoun le, which often appears even when the person is also named explicitly.

This kind of doubling is very common in Spanish:

• Le quiero mandar un mensaje a mi amiga.
• Quiero mandarle un mensaje a mi amiga.

All of these are natural.

Because with the verb mandar, Spanish normally uses a for the recipient.

• mandar algo a alguien = send something to someone

Para usually means for, and it does not fit as well here if you simply mean who receives the message.

So:

• Quiero mandar un mensaje a mi amiga. = correct
• Quiero mandar un mensaje para mi amiga. = not the normal choice for this meaning

Yes. It comes from querer (to want), which is a stem-changing verb.

The infinitive is:

• querer

But in the present tense, the e changes to ie in most forms:

• yo quiero
• tú quieres
• él/ella quiere
• nosotros queremos
• vosotros queréis
• ellos quieren

So quiero is not formed regularly from querer.

A simple pronunciation guide is:

KYEH-roh man-DAR oon men-SAH-heh ah mee ah-MEE-gah

A few helpful notes for Spain:

• quiero starts with a kye sound
• j in mensaje sounds like a strong English h
• g in amiga is a normal hard g because it comes before a

A more Spanish-like approximation:

• Quiero → KYE-ro
• mandar → man-DAR
• mensaje → men-SA-he
• amiga → a-MI-ga

Yes. Mandar can have several meanings depending on context.

Common ones include:

• to send
• to order / command
• sometimes to tell someone to do something

For example:

• Te mando un mensaje. = I’m sending you a message.
• El jefe manda. = The boss is in charge / gives orders.

In your sentence, because the object is un mensaje, the meaning is clearly to send.