Il rossetto è nella borsa accanto allo specchio.

In Italian, it is very common to use the definite article with nouns when talking about a specific thing. So il rossetto means the lipstick.

Leaving out the article would usually sound incomplete here.

• Il rossetto è nella borsa = The lipstick is in the bag
• Rossetto è nella borsa = not natural Italian

Italian uses articles more often than English does.

The article depends on the sound that follows.

Use il before most singular masculine nouns:

• il libro
• il tavolo
• il rossetto

Use lo before masculine nouns beginning with:

• s
  • consonant: lo specchio
• z: lo zaino
• ps: lo psicologo
• gn: lo gnomo
• x: lo xilofono
• y in many cases

Since rossetto begins with a normal r sound, it takes il, not lo.

È is the third-person singular form of essere (to be). Here it means is.

So:

• Il rossetto è... = The lipstick is...

Be careful: è with an accent means is.
Without the accent, e means and.

Because Italian usually combines certain prepositions with definite articles.

Here:

• in
  • la = nella

So:

• nella borsa = in the bag

This is called an articulated preposition.

A few common examples:

• nel = in + il
• nello = in + lo
• nella = in + la
• nei = in + i
• negli = in + gli
• nelle = in + le

Yes. Borsa is a feminine singular noun, so it takes:

• feminine article la
• and therefore in + la = nella

So:

• la borsa = the bag
• nella borsa = in the bag

It can mean different things depending on context. Very often borsa means:

• bag
• handbag
• sometimes purse

In this sentence, bag is a safe general translation. If the context is personal belongings, handbag could also fit well.

Accanto means next to or beside.

In this sentence:

• accanto allo specchio = next to the mirror

A useful thing to remember is that accanto is commonly used with a:

• accanto a qualcosa = next to something

So the full structure is:

• accanto a + lo specchio
• which becomes accanto allo specchio

Because accanto is followed by the preposition a, and a combines with the article lo.

Step by step:

• specchio is masculine singular
• it takes lo because it begins with sp- (an s
  • consonant cluster)
• a + lo = allo

So:

• allo specchio = to the / next to the mirror in this structure

Here it appears after accanto a, so the idea is next to the mirror.

Because specchio begins with sp-, and in Italian, masculine singular nouns beginning with s + consonant usually take lo.

Examples:

• lo specchio = the mirror
• lo studente = the student
• lo sport = the sport

That is why you get:

• lo specchio
• allo specchio
• dello specchio
• nello specchio

Yes, Italian word order is somewhat flexible, but the given order is very natural.

The sentence is structured like this:

• Il rossetto = subject
• è = verb
• nella borsa = location
• accanto allo specchio = extra detail describing where the bag is

So the meaning is:

• the lipstick is in the bag
• and the bag is next to the mirror

You could sometimes rearrange parts for emphasis, but the original version is the most neutral and natural.

Most naturally, it describes the bag.

So the sentence is understood as:

• The lipstick is in the bag that is next to the mirror

Italian, like English, can sometimes allow slight ambiguity, but in normal usage this will be interpreted as the bag being next to the mirror.

Yes. That would also be natural and would mean roughly the same thing:

• vicino allo specchio = near the mirror
• accanto allo specchio = next to / beside the mirror

Accanto usually suggests a position directly beside something.
Vicino can be a little broader and mean near.

A few useful pronunciation notes:

• rossetto: the ss is pronounced as a longer s sound than in English. The stress is on -set-: ro-SET-to.
• specchio: the sp is like in English special at the start, but the cch gives a hard k sound before io. The stress is on spec-: SPEC-chio.

Also:

• gli, gn, ch, gh, and doubled consonants often need special attention in Italian pronunciation.
• In specchio, the chi part sounds roughly like kyo.

Not naturally in this sentence. Standard Italian needs the articles here:

• Il rossetto
• nella borsa
• allo specchio

Italian sometimes drops articles in set expressions or headlines, but not in an ordinary sentence like this one.

So the full version with articles is the normal and correct choice.