Os meus amigos chegam um atrás do outro.

In European Portuguese, it is very common to use the definite article before a possessive:

• os meus amigos = my friends

For a learner of Portuguese from Portugal, os meus amigos is the most natural everyday form.
Without the article, meus amigos, the phrase is still possible in some contexts, but it is less neutral in European Portuguese.

So here:

• os = the
• meus = my
• amigos = friends

Even though English does not say the my friends, Portuguese often does.

Because it agrees with amigos.

• amigo = masculine singular
• amigos = masculine plural

So the possessive must match:

• meu amigo = my friend
• meus amigos = my friends

If the noun were feminine, it would change:

• a minha amiga = my friend
• as minhas amigas = my friends

Chegam is the 3rd person plural present indicative of chegar.

• eu chego = I arrive
• tu chegas = you arrive
• ele/ela chega = he/she arrives
• eles/elas chegam = they arrive

Since the subject is os meus amigos, the verb must be plural: chegam.

In English, this present tense can often be translated in different ways depending on context:

• My friends arrive one after another
• My friends are arriving one after another
• My friends come one after another

The present tense in Portuguese can describe:

• a general situation
• something habitual
• something happening now, depending on context

So Os meus amigos chegam um atrás do outro could mean:

• they usually arrive one after another, or
• they are arriving one after another right now

Portuguese often relies on context more than English does.

It is an expression meaning:

• one after another
• one behind the other

It describes people or things arriving in sequence, not all at once.

Literally:

• um = one
• atrás = behind
• do outro = of the other / than the other in this expression

So the literal image is one behind the other, but the natural English meaning is usually one after another.

Because um atrás do outro describes the members of the group individually, not as a whole.

So the idea is:

• friend 1 arrives
• then friend 2
• then friend 3

Each person comes one behind the other, so Portuguese uses the singular pattern um ... outro.

If the group were feminine, you would say:

• uma atrás da outra

Atrás usually means behind.

Examples:

• atrás da casa = behind the house
• atrás de mim = behind me

In this sentence, it is part of the fixed expression um atrás do outro, which can refer to physical position or sequential order. With chegam, the most natural meaning is sequential arrival:

• one after another

Because do is the contraction of:

• de + o = do

So:

• do outro = de o outro

Portuguese very often contracts prepositions with articles:

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

Here, outro takes the article o, so you get do outro.

Yes, very much so. It is a common and natural expression in Portuguese.

You can use it with people, cars, events, and more:

• Os carros passam um atrás do outro. = The cars pass one after another.
• Os alunos entram um atrás do outro. = The students go in one after another.

It is a very useful pattern to remember as a chunk.

Yes. Um a seguir ao outro is also correct and natural, and it often feels a bit more explicitly sequential.

Compare:

• um atrás do outro = one behind the other / one after another
• um a seguir ao outro = one following the other / one after another

In many contexts, both work.
With chegam, both are good:

• Os meus amigos chegam um atrás do outro.
• Os meus amigos chegam um a seguir ao outro.

The first is very common and idiomatic.

Yes. In many sentences, English might use come, while Portuguese uses chegar.

So depending on context:

• Os meus amigos chegam... can be understood as
  My friends arrive... or
  My friends come...

Portuguese focuses on the idea of reaching the destination.

It can, but with chegam, the most likely meaning is that they arrive in sequence.

So it could suggest either:

• they literally come one behind the other, or
• they simply do not all arrive at the same time

Usually, the natural interpretation is:

• They arrive one after another.

You would change the article, possessive, noun, and the expression:

• As minhas amigas chegam uma atrás da outra.

Changes:

• os → as
• meus → minhas
• amigos → amigas
• um atrás do outro → uma atrás da outra

The expression agrees with the gender of the people being referred to.

Yes. This is a very normal Portuguese sentence structure:

• Os meus amigos = subject
• chegam = verb
• um atrás do outro = adverbial expression describing how they arrive

Portuguese could sometimes vary word order for emphasis, but this version is neutral and natural.

A learner will often notice these points in European Portuguese:

• os meus amigos may sound more compressed than expected in connected speech
• chegam has a nasal ending
• atrás is stressed on the second syllable: a-TRÁS

A rough pronunciation guide is:

• Os meus amigos chegam um atrás do outro
• approximately: uz mayuz amigush shegã um atrázh du ôtru

That is only approximate, but it reflects some common European Portuguese sounds:

• unstressed vowels are often reduced
• s at the end of a word may sound like sh/zh depending on the next sound
• final -m often nasalizes the vowel before it

A useful breakdown is:

• os = the
• meus = my
• amigos = friends
• chegam = arrive / come
• um atrás do outro = one after another

If you want to learn it naturally, it is best to remember two chunks:

• os meus amigos
• um atrás do outro

That makes the sentence much easier to reuse in other contexts.