На столе лежит серебряное кольцо.

Because на can take different cases depending on the meaning:

• на стол = onto the table → motion toward a surface, so Russian uses the accusative
• на столе = on the table → location, so Russian uses the prepositional

In this sentence, the ring is already located there, so Russian uses на столе.

Compare:

• Я кладу кольцо на стол. = I put the ring onto the table.
• Кольцо лежит на столе. = The ring is lying on the table.

Столе is the prepositional singular of стол.

The basic form is:

• стол = table

After на when it means location, you usually use the prepositional case:

• на столе = on the table
• на полу = on the floor
• на полке = on the shelf

So столе is simply the form of стол required after на in a location meaning.

Russian often uses different verbs for the way something is positioned, where English often just says is.

Here, лежит comes from лежать, meaning to lie. It is used for things that are:

• lying flat
• resting on a surface
• not standing upright

A ring on a table is naturally described as лежит.

Russian commonly contrasts:

• лежать = lie
• стоять = stand
• висеть = hang

Examples:

• Книга лежит на столе. = The book is lying on the table.
• Бутылка стоит на столе. = The bottle is standing on the table.
• Картина висит на стене. = The picture is hanging on the wall.

So лежит sounds more natural than a simple is in this kind of sentence.

Yes, but it means something slightly different in feel.

• На столе лежит серебряное кольцо.
  This sounds natural and concrete: there is a silver ring there, and it is lying on the table.

• На столе есть серебряное кольцо.
  This is grammatical, but it sounds more like there is a silver ring on the table in a purely existential sense. It is less vivid and often less natural in everyday description.

Russian often prefers a posture/location verb like лежит, стоит, or висит instead of есть in sentences about physical objects in a place.

Because кольцо is the subject of the sentence.

Even though it comes after the verb, it is still the thing that лежит:

• На столе лежит серебряное кольцо.
• literally: On the table lies a silver ring.

So кольцо stays in the nominative singular.

This is very common in Russian: the sentence may begin with the location, but the noun after the verb is still the subject.

Because adjectives in Russian must agree with the noun they describe in:

• gender
• number
• case

Here the noun is кольцо, which is:

• neuter
• singular
• nominative

So the adjective must also be:

• neuter
• singular
• nominative

That gives:

• серебряное кольцо

Compare:

• серебряный стол = masculine
• серебряная ложка = feminine
• серебряное кольцо = neuter
• серебряные часы = plural

A very common clue is the ending of the noun in its dictionary form.

Кольцо ends in -о, which usually means it is neuter.

So:

• кольцо = neuter singular noun
• therefore adjectives agreeing with it take neuter forms like серебряное

This is why you get:

• новое кольцо
• большое кольцо
• серебряное кольцо

As always, there are exceptions in Russian, but -о is a strong sign of neuter gender.

Because На столе is just a location phrase, not the subject.

The true subject is серебряное кольцо, and that noun is singular, so the verb is singular too:

• лежит = singular

Word order does not change who the subject is.

If there were several rings, you would say:

• На столе лежат серебряные кольца.

So the verb agrees with кольцо / кольца, not with на столе.

Both are possible, but they emphasize different things.

• На столе лежит серебряное кольцо.
  This starts with the place, so it feels like: On the table, there is a silver ring.
  It is a natural way to introduce new information.

• Серебряное кольцо лежит на столе.
  This starts with the ring, so it feels more like you are already talking about the ring, and now you are saying where it is.

Russian word order is flexible, and it often reflects focus or what is already known vs. new.

So the original sentence is a very normal way to present a scene.

Usually серебряное кольцо means a ring made of silver.

That is the normal interpretation of серебряный / серебряное with many objects.

If you want to say silver-colored rather than made of silver, Russian might use a different adjective depending on context, for example:

• серебристый = silvery, silver-colored

So:

• серебряное кольцо = a silver ring, usually made of silver
• серебристое кольцо = a silvery-looking ring, emphasizing color/appearance

Yes, лежит is present tense.

Russian does not usually need a separate word like is in this kind of form. The single word лежит already means lies / is lying.

So:

• лежит = lies / is lying

Russian present tense often covers both:

• a simple fact
• an ongoing state

That is why one word is enough.

The stress is:

• На столе́ лежи́т серебря́ное кольцо́.

A rough pronunciation guide:

• На = nah
• столе́ = stah-LYE
• лежи́т = lye-ZHEET
• серебря́ное = see-ree-BRYA-nuh-ye
• кольцо́ = kal-TSO

The stressed syllables are important in Russian, because stress can move and is not always predictable.