Я купила новый фломастер, потому что старый уже почти не пишет.

Because купила is the past tense feminine form of купить (to buy).

• купил = he bought / I bought if the speaker is male
• купила = she bought / I bought if the speaker is female
• купило = it bought
• купили = they bought / polite you bought

So Я купила tells you that the speaker is female.

Купить is the perfective verb, which is used for a completed action: the person went and bought one new marker.

• Я купила новый фломастер = I bought a new marker (completed event)
• Я покупала новый фломастер would sound more like I was buying / I bought at some point and does not focus on the completed result in the same way

Here the important point is the result: now the speaker has a new marker.

Because фломастер is a masculine inanimate noun, and in the accusative singular, masculine inanimate nouns look the same as in the nominative.

The verb купить takes a direct object, so фломастер is in the accusative case:

• nominative: новый фломастер
• accusative: новый фломастер

They look identical here.

If it were a feminine noun, you would see a clearer change:

• новая ручка = a new pen
• Я купила новую ручку = I bought a new pen

Because both adjectives describe a masculine singular noun:

• новый фломастер = new marker
• старый (фломастер) = old one / old marker

The adjective must agree with the noun in gender, number, and case.

Here:

• masculine
• singular
• nominative/accusative form for an inanimate noun

So новый and старый both take -ый.

Russian often omits the noun when it is obvious from context. So:

• старый here means the old one
• more fully: старый фломастер

This is very natural in Russian, just like English can say:

• I bought a new marker because the old one...

Russian simply uses the adjective by itself.

Потому что means because and introduces the reason.

So the sentence structure is:

• Я купила новый фломастер = main statement
• потому что старый уже почти не пишет = reason

This is one of the most common ways to say because in Russian.

A shorter spoken alternative is sometimes так как, but потому что is the most straightforward everyday choice here.

In Russian, things like pens, pencils, markers, printers can also use verbs like писать (to write) to mean to produce writing properly.

So:

• Ручка не пишет = The pen doesn’t write / the pen isn’t working
• Карандаш плохо пишет = The pencil writes badly
• Фломастер почти не пишет = The marker barely writes

English also does this sometimes, especially with pens: This pen doesn’t write.

Because пишет is the normal active form: it writes.

• не пишет = doesn’t write / isn’t writing properly

The form пишется is a different construction and usually means something like:

• is written
• is writing itself / comes out in writing
• or appears in expressions like Как пишется это слово? = How is this word spelled/written?

For a pen or marker not working, Russian normally says:

• Ручка не пишет
• Фломастер не пишет

It means something like:

• already almost doesn’t write
• more natural English: hardly writes anymore / barely writes now

Breaking it down:

• уже = already / by now / anymore depending on context
• почти = almost
• не пишет = doesn’t write

Together, уже почти не пишет suggests the old marker is running out and now writes very badly or barely at all.

Уже often marks a change in state: by now, already, anymore.

So:

• старый почти не пишет = the old one hardly writes
• старый уже почти не пишет = the old one by now hardly writes / hardly writes anymore

It adds the sense that the marker used to work better, but now its condition has changed.

Because the sentence combines:

• a completed past action: Я купила = I bought
• with a description of the old marker’s current or ongoing condition: старый уже почти не пишет = the old one hardly writes anymore

This is normal in both Russian and English.

Compare:

• I bought a new one because the old one hardly writes anymore.

The buying happened in the past, but the problem with the old marker is presented as a present state.

Yes, that is possible, but it changes the perspective.

• не пишет = the old one hardly writes now / anymore
• не писал = the old one hardly wrote at that time / in the past

So:

• пишет connects the reason to the marker’s current condition
• писал would place that condition more firmly in the past

In many everyday situations, не пишет sounds more natural if the speaker is talking about the marker’s present state.

No, Russian word order is fairly flexible, though this version is very natural:

• Я купила новый фломастер, потому что старый уже почти не пишет.

You could also hear variations like:

• Потому что старый уже почти не пишет, я купила новый фломастер.

That version puts more emphasis on the reason.

Still, the original order is the most neutral and common for everyday speech.

Фломастер usually means a felt-tip pen / coloring marker, especially the kind used for drawing or coloring.

Маркер often means a marker pen, especially one used for highlighting, whiteboards, permanent marking, and so on.

In real life, usage can overlap, but:

• фломастер often sounds more like a children’s or drawing marker
• маркер often sounds more like a practical office or labeling marker

So новый фломастер is perfectly natural here.

Yes, Russian often drops subject pronouns when they are clear from the verb form.

So you could say:

• Купила новый фломастер, потому что старый уже почти не пишет.

That still clearly implies I bought, and because of купила, we know the speaker is female.

But я is often kept for clarity, contrast, or just normal conversational style. In this sentence, including я is completely natural.