На закате море выглядит красиво.

Not literally. In this sentence, на закате is an idiomatic time expression meaning at sunset, around sunset, or as the sun is setting.

Russian often uses на with certain time-related nouns in fixed expressions. So although на often means on, here it is best understood as at.

So:

• на закате = at sunset
• not on the sunset

Закате is in the prepositional case.

The basic form is закат = sunset.
After на in this expression, Russian uses the prepositional:

• закат → на закате

This is similar to other prepositional expressions of location or setting, and in some fixed time expressions as well.

Море is in the nominative case because it is the subject of the sentence.

The verb выглядит means looks / appears, and the thing doing that is море:

• море выглядит = the sea looks...

Also, море is a neuter noun, and its nominative singular form is море.

Because its subject, море, is singular.

The verb выглядеть means to look / to appear.
Here it is conjugated in the 3rd person singular:

• я выгляжу = I look
• ты выглядишь = you look
• он / она / оно выглядит = he / she / it looks

Since море is singular and neuter, Russian uses the same 3rd person singular form: выглядит.

The dictionary form is выглядеть.

So:

• выглядеть = to look, to appear
• выглядит = looks, appears

This is an imperfective verb and is commonly used for describing appearance.

Because красиво is an adverb, while красивое is an adjective.

In this sentence, Russian uses the pattern:

• выглядеть + adverb

So:

• выглядит красиво = looks beautiful

Even though English uses an adjective in looks beautiful, Russian often uses an adverb here.

Compare:

• красивое море = a beautiful sea
  
  • adjective describing the noun directly
• море выглядит красиво = the sea looks beautiful
  
  • adverb describing how it appears

Yes, but it means something slightly different.

• Море красивое = The sea is beautiful
• Море выглядит красиво = The sea looks beautiful

The first sounds more like a direct statement about the sea’s beauty.
The second focuses more on appearance in that moment or setting.

Because the sentence includes на закате, выглядит красиво works especially well: it suggests that at sunset, the sea appears especially beautiful.

It is possible in some contexts, but выглядит красиво is the more natural and common choice here.

Russian often uses an adverb after выглядеть:

• выглядит хорошо = looks good
• выглядит плохо = looks bad
• выглядит красиво = looks beautiful

Using an adjective-like form after выглядеть can happen, but for a simple sentence like this, красиво is the standard and easiest choice.

Because Russian has no articles.

English distinguishes:

• a sea
• the sea

Russian simply says:

• море

The exact meaning depends on context. In this sentence, English naturally translates it as the sea.

The given order is the most neutral and natural:

• На закате море выглядит красиво.

Russian word order is more flexible than English, so other orders are possible, but they change the emphasis.

For example:

• Море красиво выглядит на закате.
  This is understandable, but a bit less neutral.
• Красиво море выглядит на закате.
  This puts strong emphasis on beautifully and sounds more literary or expressive.

So the original version is a very natural default sentence.

Usually it refers more generally to the time around sunset, not a single exact second.

So it can mean:

• at sunset
• around sunset
• toward sunset
• as the sun is setting

It gives the setting or time frame rather than a mathematically exact point in time.

Вечером means in the evening, which is broader and less specific.

Compare:

• На закате море выглядит красиво.
  = The sea looks beautiful at sunset.
• Вечером море выглядит красиво.
  = The sea looks beautiful in the evening.

На закате creates a more vivid image and suggests the special light and colors of sunset.

The stresses are:

• на закАте
• мОре
• выглядИт
• красИво

Stress is important in Russian, so it helps to learn the sentence with correct pronunciation from the start.