O batom da Maria está na mala, ao lado do espelho pequeno.

Because Portuguese nouns have grammatical gender.

• batom is masculine, so it takes o
• mala is feminine, so it takes a
• espelho is masculine, so it takes o

This does not always match natural gender or English logic. You usually have to learn the noun together with its article:

• o batom
• a mala
• o espelho

That is one of the best habits for learning Portuguese vocabulary.

Da is a contraction of de + a.

So:

• de = of
• a Maria = Maria
• de + a Maria = da Maria

In European Portuguese, it is very common to use the definite article before a person’s name, especially after prepositions. So da Maria is completely natural.

In this sentence, o batom da Maria means Maria’s lipstick or literally the lipstick of Maria.

In European Portuguese, o batom da Maria is the more natural form here.

That is because names often appear with an article:

• a Maria
• o João

So after de, you usually get the contraction:

• de + a Maria = da Maria

You may sometimes hear or see de Maria, but for a learner of European Portuguese, da Maria is the safer and more idiomatic choice in sentences like this.

Because Portuguese normally uses estar for location.

• está na mala = is in the bag/suitcase

Use ser for identity, definition, or essential characteristics, and estar for position, state, or temporary condition.

So:

• O batom é vermelho. = The lipstick is red.
• O batom está na mala. = The lipstick is in the bag/suitcase.

For physical location, estar is the right verb.

Na is a contraction of em + a.

So:

• em = in
• a mala = the bag/suitcase
• em + a = na

That gives:

• na mala = in the bag/suitcase

Portuguese very often contracts prepositions with articles:

• em + o = no
• em + a = na
• de + o = do
• de + a = da
• a + o = ao
• a + a = à

Ao lado de is a fixed expression meaning beside, next to, or at the side of.

Here is the structure:

• ao = a + o
• lado = side
• de = of
• do espelho = de + o espelho

So:

• ao lado do espelho = at the side of the mirror / next to the mirror

It is best to learn ao lado de as a whole chunk.

Examples:

• ao lado da porta = next to the door
• ao lado do carro = next to the car

Because do is the contraction of de + o.

Since espelho is masculine and uses o, the phrase becomes:

• de + o espelho = do espelho

This happens automatically in normal Portuguese. You usually do not keep them separate.

In Portuguese, adjectives often come after the noun.

So:

• espelho pequeno = small mirror

This is the most neutral and common order.

English usually puts adjectives before the noun, but Portuguese often puts them after:

• casa grande = big house
• carro novo = new car
• espelho pequeno = small mirror

Yes, it can be possible, but it does not sound exactly the same.

In Portuguese, moving an adjective before the noun can make it sound:

• more literary
• more subjective
• more expressive
• sometimes less purely descriptive

So:

• espelho pequeno = a mirror that is small, neutral description
• pequeno espelho = possible, but often more stylistic or expressive

For a basic learner, noun + adjective is the safer default in cases like this.

Because the adjective must agree with the noun it describes.

Here, pequeno describes espelho, and espelho is masculine singular.

So the adjective must also be masculine singular:

• o espelho pequeno

Compare:

• o espelho pequeno = the small mirror
• a mala pequena = the small bag/suitcase

The adjective changes to match gender and number.

The comma separates an extra piece of location information.

The sentence first gives one location:

• está na mala = it is in the bag/suitcase

Then it adds a more precise detail:

• ao lado do espelho pequeno = next to the small mirror

So the comma helps break the sentence into:

1. the main statement
2. an added locational detail

In many cases, punctuation here can depend on style, rhythm, and how the speaker wants to present the information. The comma is natural and helps readability.

The structure is:

• O batom da Maria = subject
• está = verb
• na mala = location
• ao lado do espelho pequeno = extra locational detail

So it follows a very common pattern:

subject + estar + place

This is a useful pattern to reuse:

• O livro está na mesa.
• A chave está na gaveta.
• O telemóvel está ao lado do copo.

Mala often means bag or suitcase, depending on context.

So na mala could mean:

• in the bag
• in the suitcase

The exact English word depends on the situation. Since you already know the meaning in context, the important point for grammar is that mala is a feminine noun, which is why you get a mala and na mala.