Моя подруга делает котлеты из куриного фарша и ест их с салатом.

Because моя has to agree with подруга.

• подруга is a feminine singular noun
• so my must also be in the feminine singular nominative form: моя

Compare:

• мой друг = my male friend
• моя подруга = my female friend

So this is just normal adjective/pronoun agreement in Russian.

Usually, подруга means female friend.

In some contexts, it can sound like girlfriend, but that is not usually the default meaning. If someone clearly wants to mean a romantic partner, Russian often uses девушка instead.

So in a sentence like this, most learners should understand моя подруга as my female friend unless context suggests otherwise.

Because both verbs are in the 3rd person singular present tense, matching the subject моя подруга.

• делает = she does / she makes
• ест = she eats

Russian does not usually need a separate word for she in a sentence like this, because the verb form already tells you it is he/she/it singular, and the noun моя подруга tells you exactly who it is.

Yes, делать often means to do, but it can also mean to make.

With food, делать can mean make or prepare. So:

• делает котлеты = makes/prepares cutlets

Another common verb would be готовить (to cook / prepare food), but делать is still perfectly natural here.

Russian котлеты are usually not the same as an English cutlet in every context.

In Russian, котлета often means a minced-meat patty, something closer to:

• a meat patty
• a minced-meat cutlet
• sometimes even something like a small burger patty, depending on context

So котлеты из куриного фарша are chicken patties made from ground/minced chicken.

Because the preposition из normally requires the genitive case.

So:

• фарш → фарша in the genitive
• куриный must agree with фарш, so it also changes:
  • куриный → куриного

That gives:

• из куриного фарша = from ground chicken / out of chicken mince

This is a very common Russian pattern:

• из мяса = from meat
• из рыбы = from fish
• из куриного фарша = from ground chicken

Фарш means minced meat or ground meat.

So:

• куриный фарш = ground chicken / chicken mince

English speakers sometimes try to translate it too literally as stuffing, because the word can have related meanings in some contexts, but here it clearly means minced meat.

Because их is the form used for a direct object, while они is a subject form.

Here, котлеты are what she eats, so they are the object:

• она ест их = she eats them

Compare:

• они = they
• их = them

So:

• Они вкусные. = They are tasty.
• Она ест их. = She eats them.

Because их is a plural pronoun meaning them, and the nearest logical plural noun is котлеты.

So the sentence means:

• she makes the cutlets
• and eats them with salad

The pronoun avoids repeating котлеты a second time.

Because the preposition с meaning with requires the instrumental case.

So:

• салат → салатом

That is why you get:

• с салатом = with salad

This is one of the most important uses of the instrumental case in Russian:

• с супом = with soup
• с хлебом = with bread
• с салатом = with salad

Because Russian has no articles.

So котлеты can mean things like:

• cutlets
• the cutlets
• some cutlets

And салатом can mean:

• with salad
• with a salad
• with the salad

The exact meaning depends on context, not on an article word.

This is a very common thing English speakers need time to get used to.

Because the sentence describes a general action, a process, or something that can be understood as habitual or ongoing, not a single completed event.

• делает comes from делать (imperfective)
• ест comes from есть (imperfective)

If you used perfective verbs, the meaning would change:

• сделает = will make / will finish making
• съест = will eat up / will finish eating

So the imperfective is the natural choice for a neutral statement like this.

No, Russian word order is fairly flexible.

The sentence:

• Моя подруга делает котлеты из куриного фарша и ест их с салатом.

has a normal, neutral order. It starts with the subject, then the verbs and objects.

But Russian can move things around for emphasis. For example, you might hear different orders in real speech depending on what the speaker wants to stress.

Still, for learners, the original sentence is a very good standard pattern:

• subject + verb + object + additional details

No. Here с салатом means with salad, not in a salad.

So the idea is:

• she eats the cutlets
• together with salad

If you wanted to say something like in a salad, Russian would use a different structure.

Yes, grammatically it could be singular, but then other words would change too.

For example:

• Моя подруга делает котлету из куриного фарша и ест её с салатом.

Changes:

• котлеты → котлету because it is now singular and a direct object
• их → её because the pronoun must also be singular

The original sentence is plural simply because it is talking about multiple cutlets.