Я полил салат соусом.

Полил is the perfective past form of the verb полить, which means something like to pour onto / to douse / to dress in a completed way.

So Я полил салат соусом presents the action as a single completed event: the speaker poured sauce over the salad.

A related imperfective verb is поливать. If you said Я поливал салат соусом, it would sound more like:

• I was pouring sauce on the salad
• I used to pour sauce on the salad
• I poured sauce on the salad repeatedly

So полил focuses on completion, while поливал focuses on process, repetition, or ongoing action.

In Russian, the past tense is usually formed with -л.

For полить, the past tense stem gives:

• я полил — I poured/dressed
• она полила — she poured/dressed
• оно полило — it poured/dressed
• они полили — they poured/dressed

So -л is the normal marker of the past tense.

Yes. Полил is the masculine singular past form, so it normally means the speaker is male.

If the speaker were female, it would be:

• Я полила салат соусом.

This is one of the important differences from English: in the past tense, Russian verbs usually agree with the subject in gender and number.

Салат is in the accusative case, because it is the direct object of the verb: it is the thing being poured over / dressed.

For many inanimate masculine nouns, the accusative singular looks exactly like the nominative singular. That is why you see:

• nominative: салат
• accusative: салат

So even though the form does not change, the function does: here it is the object of the verb.

Соусом is the instrumental singular form of соус.

Russian often uses the instrumental case to show the means, substance, or material used in an action. Here, the sauce is what the salad is being covered with.

So:

• салат = what received the action
• соусом = what was used to do it

That is why Russian says соусом rather than using a preposition here.

Because this sentence does not mean salad with sauce as a description. It means I poured sauce over the salad.

Russian often uses the instrumental without a preposition to express what something is covered with, filled with, or treated with.

Compare:

• салат с соусом = salad with sauce (a description of the salad)
• полил салат соусом = poured sauce over the salad (an action)

So соусом without a preposition is tied to the verb and expresses the substance used in the action.

Yes. Russian word order is fairly flexible because the case endings show the grammatical roles.

The neutral order here is:

• Я полил салат соусом.

But other orders are possible, depending on emphasis:

• Салат я полил соусом. — It was the salad that I poured sauce over.
• Соусом я полил салат. — It was with sauce that I dressed the salad.

So the basic meaning stays the same, but the emphasis changes.

Russian has no articles.

So салат can mean:

• a salad
• the salad

and соусом can mean:

• with sauce
• with the sauce
• with a sauce

Which one sounds best in English depends on context. Russian leaves that to the situation rather than marking it with articles.

Sometimes, yes. Салат can mean:

• salad as a dish
• lettuce in some contexts

In this sentence, because of соусом, the most natural reading is usually salad: I poured sauce over the salad.

If the context were about vegetables in a garden or ingredients, салат could be understood as lettuce.

The main word stresses are:

• Я
• полИл
• салАт
• сОусом

So approximately:

ya pa-LEEL sa-LAHT SO-u-sam

A few notes:

• полил has stress on the second syllable: полИл
• салат has stress on the last syllable: салАт
• соусом has stress on the first syllable: сОусом

Usually, no.

• полить means to pour onto something / over something
• налить usually means to pour into something or to pour out a quantity of liquid

So:

• Я полил салат соусом = I poured sauce over the salad
• Я налил соус в миску = I poured sauce into a bowl

For salad dressing, полить is the natural choice because the liquid goes onto the salad, not into a container.