Все подпевают.

Here все means everyone or all of them.

A very common point of confusion is все vs всё:

• все = everyone / all people / all of them
• всё = everything

In normal Russian writing, the dots over ё are often omitted, so всё is frequently written as все. But in this sentence, the verb is plural: подпевают, so we know the meaning is everyone / all of them, not everything.

Because все here refers to multiple people, so Russian uses a 3rd person plural verb.

• все подпевают = everyone is singing along / all of them are singing along

Compare:

• он подпевает = he is singing along
• они подпевают = they are singing along
• все подпевают = everyone is singing along

Even though English everyone takes a singular verb (everyone sings), Russian все in this meaning behaves like a plural subject.

The infinitive is подпевать.

This verb means to sing along, to join in singing, or sometimes to provide a vocal accompaniment.

Its present-tense forms are:

• я подпеваю
• ты подпеваешь
• он / она подпевает
• мы подпеваем
• вы подпеваете
• они подпевают

So подпевают is the they form.

Петь means simply to sing.

Подпевать means to sing along or to join someone else's singing.

So:

• Все поют. = Everyone is singing.
• Все подпевают. = Everyone is singing along.

The prefix под- often adds the idea of joining in or accompanying, so подпевать suggests that the singing goes along with something already being sung or played.

It is present tense.

Подпевать is an imperfective verb, and imperfective verbs have a present tense. So:

• Все подпевают. = Everyone is singing along / Everyone sings along

Depending on context, it can mean:

• something happening right now
• something that happens regularly / habitually

For example:

• right now: Everyone is singing along
• habitual: Everyone sings along

Yes: подпеть is the perfective partner.

Very roughly:

• подпевать = imperfective, ongoing/repeated
• подпеть = perfective, one completed instance

Examples:

• Все подпевают. = Everyone is singing along.
• Все подпоют. = Everyone will join in singing / Everyone will sing along once, as a completed action

In your sentence, the imperfective подпевают is used because it describes the action as ongoing or general.

A good pronunciation guide is:

• все — roughly fsye
• подпевают — stress on ва: подпеВАют

So the full sentence sounds approximately like:

fsye pat-pye-VA-yut

A few details:

• в at the start of все sounds like f because it comes before the voiceless consonant с
• е after a soft consonant has a ye-like quality
• the stress in подпевают is on -ва-

Yes. Russian word order is flexible.

The neutral order is:

• Все подпевают.

But you could also say:

• Подпевают все.

That version puts more emphasis on все — something like It’s everyone who’s singing along or Everyone is singing along with a stronger focus.

So the basic meaning stays the same, but the emphasis changes.

Because все already functions as the subject.

Russian often does not need an extra subject pronoun when the noun or pronoun is already there. In this sentence:

• все = the subject
• подпевают = the verb

So Все подпевают is already complete and natural. Adding они would usually be unnecessary.

Yes. Все can often be translated in different ways depending on context:

• everyone
• everybody
• all
• all of them

So Все подпевают could mean:

• Everyone is singing along
• Everybody is singing along
• All of them are singing along

The best English choice depends on the situation.