Please excuse me for this, I know it's not well done but please look it over. Thanks

Hola Amigo,
Tú son invitado a una dia fiesta Valentines. En mi casa el 14 de Feburero. El fiesta empezie en desayuo y terminars en cena. Llevar los pijamas a el fiesta a el fiesta. ¡Voy a tener mariachi!
¿Regalos? Muy prefiero mucho dinero, y puede ser una pastel.
Amar,
Nacho

Oops just noticed now I made an error where "el fiesta" is written twice :/

I'll send this to our Spanish expert, SraJMcGin.

When you study Spanish, the first thing to keep in mind is: 1) gender (masculine or feminine) and 2) number (singular or plural.)

When addressing someone, a comma is required after Hola, Amigo

When studying verbs, be sure the subject and the conjugated verb match: Tú eres

gender = un día de fiesta de San Valentín.

Days of the week and months of the year are not capitalized plus check spelling in a good dictionary: febrero.

La fiesta empieza (a stem-changing verb e--->ie and it's an -ar verb)

con un desayuno (spelling) y termina con una cena.

Here is a place for a familiar tú com mand = Lleva

a + el = al BUT this word is feminine = a la fiesta.

Probably you will have more than one mariachi? = mariachis.

Drop "Muy" = Yo prefiero.....un pastel (gender)

Con amor (one possibility but not the infinitive amar = to love)

May I suggest that you rewrite the entire paragraph, to be sure you have corrected all the errors. I'll flag this and come back later to check.

Sra

Dear Nacho,

Thank you for inviting me to your Valentine's Day party at your house on February 14th. I appreciate your kind invitation. I understand that the party will begin with breakfast and end with dinner, and it sounds like a wonderful celebration. You mentioned that guests should bring pajamas to the party, which is an interesting and fun idea. I'm particularly excited about the fact that you'll have a mariachi band at the party!

In terms of gifts, you mentioned that you would greatly prefer money as a gift, and a cake is also a suitable option. It's always helpful to have some guidance on what the host prefers as a gift.

Thank you again for the invitation, and I look forward to celebrating Valentine's Day with you.

Sincerely,
[Your Name]