Я взяла один бублик в дорогу, потому что его удобно есть.

Взяла is the past tense, feminine singular form of взять (to take).

Russian past tense agrees with the subject in gender and number:

• я взял = I took (said by a man)
• я взяла = I took (said by a woman)

So this sentence is spoken by a female speaker.

The verb взять is perfective, so it refers to a completed action: to take, to pick up, to take along.

Its past tense feminine form is взяла.

In this sentence, the idea is that the speaker took a bagel along for the trip as a finished, one-time action. If you used the imperfective брала, it would sound more like a repeated action, a process, or context-dependent background information.

Yes, один literally means one, but in real Russian it can do more than just count.

Here один бублик can mean:

• one bagel
• a single bagel
• sometimes just a bagel, with a slight emphasis on quantity

So the speaker is specifying that she took exactly one bagel.

Without один, Я взяла бублик в дорогу would also be possible and would simply mean I took a bagel for the trip.

Because бублик is the direct object of взяла, it is in the accusative case.

However, бублик is a masculine inanimate noun, and for masculine inanimate nouns, the accusative singular looks the same as the nominative singular.

So:

• nominative: один бублик
• accusative: один бублик

That is why the form does not visibly change here.

If the noun were animate, the accusative would often look different.

В дорогу is an idiomatic expression meaning something like:

• for the road
• for the trip
• to take along on the journey

So Я взяла один бублик в дорогу means the speaker took the bagel along to eat while traveling.

Literally, в usually means into, and дорогу is the accusative of дорога (road, way, journey), but here the whole phrase works idiomatically rather than literally.

Because в can take either the accusative or the prepositional case, depending on meaning.

• в + accusative often expresses direction or movement toward something
• в + prepositional often expresses location

Compare:

• в дорогу = for the journey / onto the road / on the trip
• в дороге = on the road / while traveling

In this sentence, в дорогу is a set expression meaning for the trip, so the accusative дорогу is used.

Его refers back to бублик.

Here it is the direct object of есть (to eat), so it is in the accusative case:

• бублик = bagel
• его = it / him in accusative form

Since бублик is masculine singular, the pronoun used is его.

So его удобно есть literally means it is convenient to eat it.

In natural English, that becomes something like it’s easy/convenient to eat.

Because он is nominative case, used for the subject of a clause.

But in его удобно есть, the bagel is not the subject of есть. It is the object: you eat it.

So Russian needs the accusative form его, not nominative он.

Compare:

• Он вкусный. = It is tasty. / He is tasty.
• Я ем его. = I eat it.

Удобно here is an adverb and is part of an impersonal construction:

• удобно есть = it is convenient to eat
• удобно носить = it is convenient to wear/carry
• удобно читать = it is convenient/easy to read

Russian often uses short impersonal words like удобно, трудно, легко, интересно with an infinitive.

Удобный is an adjective meaning comfortable or convenient, but it would need to describe a noun directly:

• удобный стул = a comfortable chair
• удобный бублик would sound odd

So удобно is correct because the sentence means it is convenient to eat it, not it is a convenient bagel.

Because after impersonal words like удобно, Russian often uses the infinitive to express a general action.

So:

• удобно есть = it is convenient to eat
• удобно пить = it is convenient to drink
• удобно брать с собой = it is convenient to take with you

This structure does not name a specific person doing the action; it presents the action in a general way.

Yes. Потому что is a common way to say because.

So the sentence structure is:

• Я взяла один бублик в дорогу = main clause
• потому что его удобно есть = reason clause

Russian normally puts a comma before потому что, just as English often separates the because clause in writing when it follows the main clause.

Yes. Russian word order is flexible, although different orders change emphasis.

The given sentence is natural and neutral:

• Я взяла один бублик в дорогу, потому что его удобно есть.

You could also hear variations like:

• В дорогу я взяла один бублик, потому что его удобно есть.
  Emphasis on for the trip
• Я взяла в дорогу один бублик, потому что его удобно есть.
  Also natural; the phrase в дорогу is placed a bit earlier

The basic meaning stays the same, but the focus shifts slightly depending on what the speaker wants to highlight.

Yes, it is natural Russian.

A very literal translation, it is convenient to eat it, sounds somewhat awkward in English, but in Russian this is a normal way to express the idea that a food item is easy or handy to eat.

So the meaning is more like:

• because it’s easy to eat
• because it’s convenient to eat
• because it’s handy to eat on the go

Russian often keeps the object pronoun in this kind of structure even where English might drop it.