Por la mañana, el hombre dice buenos días.

In Spain, por la mañana is the most natural and standard way to say in the morning.

It literally means something like during the morning. Spanish uses this pattern a lot:

• por la mañana = in the morning
• por la tarde = in the afternoon/evening
• por la noche = at night/in the evening

You may hear en la mañana in some varieties of Spanish, but for Spain, por la mañana is the safest choice.

Because this is a fixed expression. In Spanish, parts of the day often appear with the definite article:

• la mañana
• la tarde
• la noche

So after por, Spanish normally says:

• por la mañana
• por la tarde
• por la noche

Even though English says in the morning without thinking much about the article, Spanish naturally includes it here.

Spanish usually needs an article before a singular countable noun in this kind of sentence.

So:

• el hombre = the man
• un hombre = a man

Just hombre by itself would usually sound incomplete here.

If you are talking about a specific man, el hombre is correct. If you were introducing him for the first time as a man, you would normally say un hombre.

Dice is the he/she/it form of decir, which means to say.

The infinitive is:

• decir = to say

Present tense:

• yo digo = I say
• tú dices = you say
• él/ella dice = he/she says

Since the subject is el hombre, you need the he form: dice.

Because decir is used when you give the actual words someone says.

• dice buenos días = he says good morning

Hablar means to speak or to talk, but it is not normally used to introduce the exact greeting itself in this way.

Compare:

• El hombre dice buenos días. = The man says good morning.
• El hombre habla. = The man speaks / is talking.

So if you want to report the greeting itself, decir is the right verb.

Because buenos días is a fixed greeting in Spanish.

Spanish greetings for times of day are normally plural:

• buenos días
• buenas tardes
• buenas noches

Even though English uses singular good morning, Spanish does not. In Spain, buenos días is the normal form.

Normally, no. In standard Spanish, greetings are not capitalized unless they begin the sentence.

So in the middle of a sentence, you write:

• El hombre dice buenos días.

But if the greeting starts the sentence, then the first word is capitalized in the normal way:

• Buenos días.

The comma separates the opening time expression from the rest of the sentence.

• Por la mañana, el hombre dice buenos días.

This is similar to English when you begin with something like In the morning, ...

In Spanish, that comma is very natural here, especially because por la mañana is an introductory phrase. In a very short sentence, some writers might omit it, but keeping it is a good choice.

In most of Spain, dice is pronounced roughly DEE-theh, with the c before e sounding like the th in think.

So:

• dice ≈ DEE-theh

More exactly: /ˈdi.θe/

Also, in hombre, the h is silent:

• hombre ≈ OM-breh

So the full sentence in standard Peninsular Spanish sounds roughly like:

• Por la mañana, el hombre di-the buenos días.

Yes, but it changes the punctuation and slightly changes the feel.

• El hombre dice buenos días.
  This reports the greeting naturally as part of the sentence.

• El hombre dice: buenos días.
  This introduces the exact words more directly, almost like a quotation or announcement.

In everyday simple narration, El hombre dice buenos días is completely normal.