На столе уже стоит большая салатница, потому что гости скоро придут.

Because Russian uses different cases depending on whether you mean location or movement toward a place.

• на столе = on the table / at the table as a location
  
  • на + prepositional case
• на стол = onto the table
  
  • на + accusative case

In this sentence, the bowl is already located on the table, so Russian uses the prepositional:

• На столе уже стоит... = On the table there is already...

Compare:

• Я ставлю салатницу на стол. = I am putting the salad bowl onto the table.
• Салатница стоит на столе. = The salad bowl is standing on the table.

Russian often uses position verbs where English would simply say is.

Here, стоит literally means stands, but in Russian it is very natural for certain objects, especially containers or upright objects, to stand somewhere.

So:

• салатница стоит на столе = literally the salad bowl stands on the table
• natural English translation: the salad bowl is on the table

Russian commonly distinguishes:

• стоит = stands upright
• лежит = lies flat
• висит = hangs
• сидит = sits (for people, animals, and sometimes certain objects in set expressions)

A bowl, vase, bottle, cup, etc. can often стоять if it is resting upright on a surface.

Usually, no—not in the way English learners often expect.

Russian does not normally use a present-tense verb meaning is/are in simple sentences like this. Instead, it either leaves it out or uses a more specific verb such as стоит, лежит, висит, etc.

So Russian prefers:

• На столе стоит большая салатница.

rather than something like:

• На столе есть большая салатница.

Есть can sometimes mean there is/there are, but here it sounds less natural because Russian prefers the more concrete verb стоит for an object placed on a table.

Уже means already.

In this sentence:

• На столе уже стоит большая салатница
  = There is already a large salad bowl on the table

It suggests preparation has begun before the guests arrive.

Its placement is flexible, but the position can slightly affect emphasis. Here, уже comes before the verb стоит, which is very natural.

Compare:

• На столе уже стоит большая салатница.
  Neutral: the bowl is already there.
• Уже на столе стоит большая салатница.
  More emphasis on already.
• Большая салатница уже стоит на столе.
  More emphasis on the bowl itself.

Because the adjective must agree with the noun in gender, number, and case.

Here:

• салатница is feminine
• it is singular
• it is the subject, so it is in the nominative case

Therefore the adjective большой becomes:

• большая

So:

• большая салатница = a big/large salad bowl

Agreement pattern here:

• masculine: большой стол
• feminine: большая салатница
• neuter: большое окно
• plural: большие гости would be grammatical in form, though odd in meaning

Салатница is a noun meaning salad bowl, usually a bowl used for serving salad.

It comes from:

• салат = salad
• the suffix -ница, which often forms nouns for containers or related objects

So салатница is more specific than just миска (bowl) or чаша (bowl/cup, more literary or stylistic).

In this sentence, большая салатница suggests a fairly large serving bowl set out for guests.

Because потому что is the normal way to say because when introducing a reason clause.

So:

• ..., потому что гости скоро придут.
  = ..., because the guests will arrive soon.

On its own, потому usually means something more like that’s why / for that reason, and it is often paired with поэтому in logic or explanation.

Compare:

• Я ушёл, потому что устал. = I left because I was tired.
• Я устал, поэтому я ушёл. = I was tired, so I left.

So in your sentence, потому что is exactly what you want.

Придут is the future tense of the perfective verb прийти (to arrive / to come).

Russian uses perfective future when talking about a single completed future event. Here, the guests are expected to arrive soon as one event.

• гости скоро придут = the guests will arrive soon

Why not the others?

• приходят = present tense / habitual meaning
  This would mean something like they come / they are coming regularly, which does not fit here.
• будут приходить = imperfective future
  This suggests repeated or ongoing arrivals, more like will be coming (one after another / repeatedly).

Since the sentence refers to one expected arrival event, придут is the natural choice.

Придут is:

• verb: прийти = to come / to arrive
• aspect: perfective
• tense: future
• person: 3rd person
• number: plural

So it agrees with гости (guests), which is plural:

• гость = guest
• гости = guests

Conjugation idea:

• я приду = I will come
• ты придёшь = you will come
• он/она придёт = he/she will come
• мы придём = we will come
• вы придёте = you will come
• они придут = they will come

Гости is nominative plural, because it is the subject of the verb придут.

• гость = guest
• гости = guests

In the clause:

• гости скоро придут

the guests are the ones performing the action of arriving, so nominative is required.

No, Russian word order is fairly flexible, but changing it changes the focus or emphasis.

The original sentence:

• На столе уже стоит большая салатница, потому что гости скоро придут.

This sounds natural and neutral.

Other possible orders:

• Большая салатница уже стоит на столе...
  Emphasizes the salad bowl
• Уже на столе стоит большая салатница...
  Emphasizes already
• Гости скоро придут, поэтому на столе уже стоит большая салатница.
  Same basic meaning, but the reason/result order is reversed

So the original order is not the only possible one, but it is a very normal one.

Starting with На столе puts the setting/location first.

Russian often begins sentences with the place where something is located, especially when introducing what is there:

• На столе стоит салатница.
• На стене висит картина.
• На полке лежит книга.

This is similar to English patterns like:

• On the table, there is a bowl
• On the wall hangs a painting

In natural English, we often translate more smoothly as:

• There is already a large salad bowl on the table...

So Russian is foregrounding the location first.

Yes. Скоро means soon, and its position can move somewhat.

The most neutral version here is:

• гости скоро придут

But you may also hear:

• скоро гости придут
• гости придут скоро

The last version can sound a little more marked or conversational depending on context.

Usually:

• гости скоро придут = neutral, standard
• скоро гости придут = stronger emphasis on soon

Both are possible, but large often sounds a little more natural in English for a serving bowl.

• большая салатница = a big salad bowl
• большая салатница = a large salad bowl

The Russian adjective большой / большая / большое / большие covers both big and large, so the exact English choice depends on style.

Yes, that implication is very strong.

The combination of:

• уже = already
• потому что = because
• гости скоро придут = the guests will arrive soon

makes it sound like someone has begun preparing the table in advance. So even though the sentence literally just states that the bowl is on the table, it naturally suggests:

• it has been placed there in preparation
• the household is getting ready for the guests

That kind of practical implication is very common in Russian, just as it is in English.