Мука лежала на верхней полке, и мне пришлось встать на стул, чтобы достать её.

Because мука is the subject of the first clause, so it is in the nominative case.

• мука = flour
• лежала = was lying / was sitting / was located

So Мука лежала... literally means The flour was lying...

Also note that мука is a feminine singular noun, and that affects the verb form too.

In the past tense, Russian verbs agree with the subject in gender and number.

Since мука is:

• feminine
• singular

the verb must be лежала.

Compare:

• стол лежал = the table was lying
• книга лежала = the book was lying
• письмо лежало = the letter was lying
• вещи лежали = the things were lying

So мука лежала is correct because мука is feminine.

Russian often uses лежать much more naturally than English uses to lie.

лежать can mean:

• to be lying
• to be located
• to be sitting somewhere

So Мука лежала на верхней полке means something like:

• The flour was on the top shelf
• more literally: The flour was lying on the top shelf

This is a very normal Russian way to describe where an object is.

Because this phrase describes location, not movement.

With на:

• на + prepositional = on somewhere, location
• на + accusative = onto somewhere, movement toward a surface

Here the flour is already there, so we use location:

• на верхней полке = on the top shelf

Compare:

• Мука лежала на верхней полке. = The flour was on the top shelf.
• Я поставил муку на верхнюю полку. = I put the flour onto the top shelf.

So:

• полке = prepositional singular
• верхней = adjective agreeing with полке

Because верхней must agree with полке, which is:

• feminine
• singular
• prepositional case

The dictionary form is верхний = upper / top

Its feminine forms include:

• nominative: верхняя
• accusative: верхнюю
• prepositional: верхней

Since the sentence says on the upper shelf and that requires the prepositional case, we get:

• на верхней полке

Мне пришлось is a very common Russian way to say I had to or I ended up having to.

It comes from прийтись / приходиться, which often works as an impersonal construction:

• мне пришлось = I had to
• literally: it fell to me / it turned out that I had to

Why мне? Because the person affected by this necessity is put in the dative case.

So:

• мне пришлось встать на стул = I had to stand on a chair

This is a bit different from я должен был:

• я должен был = I was supposed to / I was obliged to
• мне пришлось = I had to, due to circumstances

In this sentence, мне пришлось sounds very natural because the situation forced the action.

Here пришлось means had to.

It is the past tense of прийтись, the perfective partner of приходиться.

A useful contrast:

• мне приходилось = I used to have to / I would have to / I had to repeatedly
• мне пришлось = I had to once, in this particular situation

So in this sentence, the speaker is referring to one completed situation: the flour was high up, so I had to stand on a chair.

Because встать means to stand up / get onto one’s feet, while стоять means to be standing.

Here the sentence focuses on the action needed:

• first, the speaker got onto the chair / stood on it
• then, they were able to reach the flour

So:

• встать на стул = to stand on a chair / get up onto a chair
• стоять на стуле = to be standing on a chair

Russian often uses встать на... for getting onto something in order to stand there.

Because this is again movement toward a surface, not static location.

With на:

• на стуле = on the chair, location
• на стул = onto the chair, movement

In мне пришлось встать на стул, the speaker moves onto the chair, so Russian uses the accusative:

• стул = accusative singular, same form as nominative for an inanimate masculine noun

Compare:

• Я стою на стуле. = I am standing on the chair.
• Я встал на стул. = I stood up onto the chair.

Because чтобы introduces a purpose clause: in order to, so that.

So:

• чтобы достать её = in order to reach/get it

When the subject is the same as in the main clause, Russian very often uses:

• чтобы + infinitive

Examples:

• Я пришёл, чтобы помочь. = I came to help.
• Он открыл окно, чтобы проветрить комнату. = He opened the window to air out the room.

Here the subject is still the speaker, so:

• мне пришлось встать на стул, чтобы достать её = I had to stand on a chair in order to reach/get it

Because достать is perfective, and the sentence refers to a single completed goal.

• доставать = to be reaching for / to get repeatedly / to take out in an ongoing or habitual sense
• достать = to reach / get / retrieve successfully, one completed action

Here the meaning is:

• the speaker stood on the chair so as to manage to reach the flour

That completed result fits достать very well.

Compare:

• Я не мог достать книгу. = I couldn’t reach the book.
• Я доставал книги с верхней полки каждый день. = I used to take books down from the top shelf every day.

In this sentence, достать can suggest several closely related ideas:

• reach
• get hold of
• take down

Because the flour is on a high shelf, the practical meaning is something like:

• to reach it
• possibly also to get it down

Russian достать often covers this whole idea of successfully getting something that is difficult to reach.

So чтобы достать её could be translated naturally as:

• to reach it
• to get it down depending on context.

Because её refers back to мука, which is a feminine noun.

It is the accusative form of она when used as a direct object:

• она = she / it
• её = her / it

Here the flour is the thing being reached, so it is the direct object:

• достать её = reach it / get it

Even though English uses it, Russian still has to choose a grammatical gender, and because мука is feminine, the pronoun is feminine too.

Yes. In normal Russian writing, ё is often replaced by е, so you may also see:

• ее

But the pronunciation and meaning are the same here:

• её = ее

Using ё is clearer for learners, because it shows the stress and correct pronunciation.

That is the normal neutral word order in Russian:

• verb + object

So:

• достать её = reach it / get it

Russian word order is flexible, but the basic order here is the most natural one.

You could move things around for emphasis in some contexts, but in a standard sentence достать её is exactly what you would expect.

Because Russian has no articles like the or a/an.

Whether something is definite or indefinite is understood from context.

So:

• на верхней полке can mean on the top shelf
• in another context it could also feel closer to on an upper shelf

In this sentence, English naturally uses the because the speaker has a particular shelf in mind, but Russian does not need an article to express that.

Not normally in this context.

• встать = perfective, one completed action
• вставать = imperfective, repeated or ongoing action, or focus on process

Since the speaker had to do this once, the perfective встать is the natural choice:

• мне пришлось встать на стул = I had to stand on a chair

If you said пришлось вставать, it would usually suggest a different nuance, such as repeated action or more focus on the process in a broader context.

Here верхней most naturally means upper or top.

• верхний = upper / top
• самый верхний = the very top / the highest one

So:

• на верхней полке = on the top shelf or on the upper shelf

In this sentence, top shelf is the most natural English translation, even though the Russian adjective itself is literally closer to upper/top than to highest.