Από τη βεράντα του ξενοδοχείου φαινόταν η θάλασσα και ο ορίζοντας ήταν γεμάτος σύννεφα.

Not necessarily. Από usually means from, but here it gives the viewpoint: from the hotel veranda / from the hotel balcony.

So Από τη βεράντα του ξενοδοχείου means something like seen from the hotel veranda or from the hotel veranda, .... It is about where the view is from, not about someone physically moving away from the veranda.

A useful contrast:

• Από τη βεράντα = from the veranda
• Στη βεράντα = on / at the veranda

Because βεράντα is the object of the preposition από, so it must be in the accusative case.

The dictionary form is:

• η βεράντα = nominative, the veranda

After από, it becomes:

• τη βεράντα = accusative, the veranda

For many feminine nouns in -α, the noun itself looks the same in nominative and accusative, so the main visible change is in the article:

• η βεράντα
• τη βεράντα

In Modern Greek, the accusative feminine article is underlyingly την, but the final -ν is often dropped before many consonants.

So before β in βεράντα, the normal form is:

• τη βεράντα

You will often see this pattern:

• τη θάλασσα
• τη μέρα
• τη βεράντα

But the -ν is usually kept before vowels and certain consonants.

Because Greek uses the genitive to show possession or close relation.

• το ξενοδοχείο = the hotel
• του ξενοδοχείου = of the hotel

So:

• η βεράντα του ξενοδοχείου = the hotel’s veranda / the veranda of the hotel

This is a very common Greek structure:

• η πόρτα του σπιτιού = the door of the house
• το χρώμα του αυτοκινήτου = the color of the car

Φαινόταν is the imperfect, 3rd person singular form of φαίνομαι.

Here it means:

• was visible
• could be seen
• appeared

So:

• φαινόταν η θάλασσα = the sea was visible / you could see the sea

A useful point: φαίνομαι has middle/passive-looking endings, but it is often used with an active-style meaning in English.

Because Greek word order is more flexible than English word order.

In English, you usually expect:

• the sea was visible

In Greek, both of these are possible:

• Η θάλασσα φαινόταν
• Φαινόταν η θάλασσα

The version in your sentence sounds very natural in description. It helps set the scene first, almost like:

• From the hotel veranda, there was the sea in view...

Even though η θάλασσα comes after the verb, it is still the subject because it is in the nominative.

Because the sentence is describing a background scene in the past.

The imperfect is often used for:

• ongoing situations
• descriptions
• background details
• states that lasted for some time

So here the speaker is painting a picture:

• the sea was visible
• the horizon was full of clouds

If Greek used an aorist instead, the meaning would feel more like a single event or change:

• φάνηκε = appeared / came into view
• γέμισε = filled up / became full

But this sentence is not about sudden events. It is about how the scene looked.

Because the sentence actually has two separate clauses joined by και:

1. Από τη βεράντα του ξενοδοχείου φαινόταν η θάλασσα
2. και ο ορίζοντας ήταν γεμάτος σύννεφα

So the first verb, φαινόταν, belongs only to η θάλασσα.

The second clause has its own subject and verb:

• ο ορίζοντας ήταν...

That is why both verbs are singular.

Γεμάτος is an adjective, and it must agree with ο ορίζοντας.

• ο ορίζοντας = masculine singular nominative
• so the adjective must also be masculine singular nominative:
  • γεμάτος

Compare:

• ο ορίζοντας ήταν γεμάτος = masculine singular
• η θάλασσα ήταν γεμάτη = feminine singular
• τα σύννεφα ήταν γεμάτα = neuter plural

So the form γεμάτος is chosen because it describes ο ορίζοντας.

In Greek, γεμάτος can be followed directly by the thing that fills something.

So:

• γεμάτος σύννεφα = full of clouds

Here:

• σύννεφα is the plural of σύννεφο = cloud
• it means the horizon was filled with clouds

Greek can also use other patterns, such as:

• γεμάτος από σύννεφα
• γεμάτος με σύννεφα

But the simple direct pattern γεμάτος σύννεφα is very common and natural.

Also note that σύννεφα is neuter plural, and in the neuter plural the nominative and accusative have the same form.

Greek uses the definite article more often than English, especially when talking about specific things in a scene.

Here the speaker means the visible sea and the visible horizon in that setting, so Greek naturally says:

• η θάλασσα
• ο ορίζοντας

This is very normal in descriptive Greek. Even when English sometimes sounds fine without an article in a poetic or compressed style, Greek often prefers the article with concrete, identifiable nouns.