Портной укоротил и подшил рукава.

Because портной is one of those Russian nouns that historically look like adjectives but function as nouns.

Here, Портной is:

• masculine
• singular
• nominative case
• the subject of the sentence

So in this sentence it means the tailor.

Its forms decline a lot like an adjective:

• nominative: портной
• genitive: портного
• dative: портному
• accusative: портного (because it is animate)
• instrumental: портным
• prepositional: о портном

So even though it looks adjective-like, you should learn it as a normal noun meaning tailor.

That -л is the usual marker of the past tense in Russian.

Both verbs are:

• past tense
• masculine
• singular

Russian past tense agrees with the subject in gender and number:

• masculine: укоротил
• feminine: укоротила
• neuter: укоротило
• plural: укоротили

Since портной is masculine singular, the verbs are masculine singular too:

• Портной укоротил и подшил рукава.

Because in Russian, past-tense verbs agree with the subject, not the object.

The subject is Портной = the tailor, which is:

• masculine
• singular

So both verbs must also be:

• masculine
• singular

The object рукава being plural does not affect the verb form.

Рукава is the correct form here because it is the accusative plural of рукав (sleeve) for an inanimate noun.

For inanimate masculine nouns, the accusative plural is the same as the nominative plural.

So:

• singular nominative: рукав
• plural nominative: рукава
• plural accusative: рукава
• plural genitive: рукавов

In this sentence, рукава is the direct object of the two verbs, so accusative plural is needed.

Some masculine nouns in Russian form their plural in -а / -я rather than -ы / -и. Рукав is one of them.

So:

• singular: рукав
• plural: рукава

This is just something to memorize as part of the noun’s pattern. A lot of everyday nouns do this:

• город → города
• берег → берега
• рукав → рукава

Both verbs are perfective.

That means the sentence presents the actions as completed results:

• the tailor shortened them
• and hemmed them

That fits very naturally here, because the sentence describes a finished alteration.

Their imperfective counterparts would be:

• укорачивать / укорачивать
• подшивать

If you used imperfective past, it would sound more like process, repetition, or background:

• Портной укорачивал и подшивал рукава. = The tailor was shortening and hemming the sleeves / used to shorten and hem sleeves.

They describe two different actions:

• укоротил = shortened
• подшил = hemmed, took up, or stitched the edge after shortening

So the sentence implies a typical clothing alteration:

1. the sleeves were made shorter
2. then the edge was sewn properly

In clothing contexts, подшить often means something like:

• to hem
• to take up
• to sew up the edge neatly after altering

Russian has no articles like the or a/an.

So Портной can mean:

• a tailor
• the tailor

And рукава can mean:

• sleeves
• the sleeves

Which one is meant depends on context. In a normal sentence like this, English usually needs the, but Russian does not.

Because Russian often leaves possession unstated when it is obvious from context.

So рукава here simply means the sleeves, and Russian does not have to say:

• его рукава
• у пиджака рукава
• рукава пальто

If the context already makes it clear which garment is being discussed, just рукава is enough.

English often also does this:

• The tailor shortened the sleeves.

Because и is joining two verbs with the same subject:

• укоротил
• подшил

This is a simple coordination:

• Портной укоротил и подшил рукава.

No comma is needed.

A comma would appear only in more complicated structures, for example if there were separate clauses with different subjects or extra inserted material.

No, Russian word order is relatively flexible.

Портной укоротил и подшил рукава is the most neutral order:

• subject + verbs + object

But other orders are possible for emphasis:

• Рукава портной укоротил и подшил.
  Focuses more on the sleeves
• Укоротил и подшил рукава портной.
  Can sound literary or strongly contrastive

The original order is the best default one for learners.

The main stresses are:

• портно́й
• укороти́л
• подши́л
• рукава́

So a good pronunciation guide is:

портно́й укороти́л и подши́л рукава́

A rough English-style approximation:

• par-TNOY
• oo-ka-ra-TEEL
• pat-SHEEL
• roo-ka-VA

But it is better to follow the Russian stress pattern than English approximations.

Not usually in this context.

The basic verb шить means to sew.
But подшить has a more specific meaning, especially with clothing:

• to hem
• to take up
• to stitch the edge underneath
• sometimes to alter by sewing

So in this sentence, подшил рукава is more specific than simply sewed the sleeves. It refers to finishing or adjusting them properly after shortening.

Yes. That is completely normal.

In Портной укоротил и подшил рукава, the direct object рукава applies to both verbs:

• shortened the sleeves
• hemmed the sleeves

Russian often avoids repeating the object when the meaning is clear.

Repeating it would sound unnecessarily heavy:

• Портной укоротил рукава и подшил рукава.

So the original version is the natural one.