На собеседование нас попросили заходить поодиночке.

Because на + accusative often shows direction toward a place or event.

• на собеседование = to the interview
• на собеседовании = at the interview

Here the sentence is about being told how to go in for the interview, so Russian uses на собеседование.

Because попросить uses the pattern:

попросить кого? сделать что?
= to ask someone to do something

So:

• нас попросили = they asked us
• нам попросили would be wrong here
• мы would only be used as the subject, but here we/us is the object of asked

So the structure is literally:

[Someone] asked us to enter one by one.

Попросили is the past plural form of попросить.

Russian often leaves out the subject when it is unknown, obvious, or unimportant. So попросили by itself can mean something like:

• they asked
• someone asked
• we were asked (in natural English translation)

In this sentence, the important thing is not exactly who asked, but the instruction itself.

Because English often prefers a passive translation here, while Russian uses an active structure with an omitted subject.

Literally:

• нас попросили = they asked us

Naturally in English:

• we were asked

Both mean the same thing in this context. Russian does this very often.

Here заходить means to go in, to enter, or to come in.

It comes from заходить / зайти, which can mean entering a room or going inside somewhere.

In this sentence, it suggests entering the room where the interview is taking place, one person at a time.

So:

• заходить поодиночке = to go in one by one

Both verbs can relate to entering, but заходить is very common in everyday speech for coming in / going in, especially through a doorway.

• заходить often sounds natural and conversational
• входить can sound a bit more formal or more focused on the act of entering itself

In this sentence, заходить is the most natural choice for going in for the interview.

Because the sentence is about an instruction or procedure, not just one single completed act.

Imperfective is common after verbs like просить, especially when talking about:

• general instructions
• repeated actions
• the manner in which something should happen

Here, several people are being told how to enter: one by one. That repeated/sequential idea fits заходить very well.

Compare:

• попросили заходить поодиночке = they asked us to go in one by one / that we should enter one by one
• попросили зайти = they asked us to go in / come in (more like a single completed act)

Поодиночке means:

• one by one
• individually
• separately

It describes how people should do the action: not together, but each person alone.

So:

• заходить поодиночке = to go in one at a time

It is a normal, common word. You can use it in both everyday and fairly formal situations.

For example:

• Дети заходили поодиночке. = The children came in one by one.
• Нас вызывали поодиночке. = We were called in one by one.

So it fits well with a sentence about an interview.

It sets the context right away:

На собеседование = as for the interview / for the interview

Starting with it highlights the situation first:

• На собеседование нас попросили заходить поодиночке.
• Literally: For the interview, we were asked to go in one by one.

Russian word order is flexible, so putting this phrase first is natural.

Yes, that would also be grammatical, but it sounds a little less neat.

The original sentence:

На собеседование нас попросили заходить поодиночке.

puts the setting first, which is very natural in Russian.

Your version is understandable, but the original has better flow and emphasis.

A useful breakdown is:

• На собеседование = to the interview
• нас = us
• попросили = asked
• заходить = to go in / enter
• поодиночке = one by one

So literally:

To the interview, they asked us to go in one by one.

Natural English:

We were asked to go in to the interview one by one.