اليوم نسيت مظلتي في الحافلة، ولذلك اشتريت ملابس جديدة من المتجر.

اليوم means today, and it is being used as a time expression.

In Arabic, time expressions often come at the beginning of the sentence to set the scene:

• اليوم نسيت مظلتي... = Today, I forgot my umbrella...

This is very natural in Arabic. You do not need a word like في before اليوم here.

A fully vocalized form would usually be اليومَ because it functions as an adverb of time.

Because the verbs already show the subject.

• نسيت = I forgot
• اشتريت = I bought

In Arabic, subject pronouns are often omitted when the verb already makes the subject clear. Adding أنا is possible, but it adds emphasis:

• أنا نسيت مظلتي = I forgot my umbrella

Without أنا, the sentence is more neutral and natural.

That ending marks the first person singular in the past tense.

So:

• نسيت = I forgot
• اشتريت = I bought

If fully vocalized, they are:

• نَسِيتُ
• اشْتَرَيْتُ

In normal Arabic writing, short vowels are usually not written, so you see نسيت and اشتريت without the final ـُ.

مظلتي means my umbrella.

It is made from:

• مظلة = umbrella
• ـي = my

So:

• مظلة + ي = مظلتي

An important detail: the final ة (taa marbuuTa) changes in pronunciation when a suffix is attached. Instead of sounding silent, it becomes a clear t sound:

• مظلة = miẓalla(h)
• مظلتي = miẓallatī

So the word is not just umbrella + my mechanically; the shape and pronunciation adjust a little.

Arabic usually uses في with buses, cars, trains, and similar vehicles:

• في الحافلة = on/in the bus
• في السيارة = in the car
• في القطار = on/in the train

English often says on the bus, but Arabic commonly uses في, which literally looks like in.

If you said على الحافلة, it would sound more like on top of the bus, which is not the intended meaning.

ولذلك means and therefore, so, or for that reason.

It is made of:

• و = and
• لذلك = therefore / for that reason

So the sentence links the two actions like this:

• I forgot my umbrella on the bus, therefore I bought new clothes from the store.

It is a formal, very standard connector in Modern Standard Arabic.

Yes.

• لذلك اشتريت... = Therefore, I bought...
• ولذلك اشتريت... = And therefore, I bought...

Both are correct. The version with و feels smoothly connected to the previous clause, especially after a comma. In formal writing, ولذلك is very common.

من usually means from, and here it shows the source/place of purchase:

• اشتريت ملابس جديدة من المتجر = I bought new clothes from the store

This is a very normal use of من in Arabic.

You could also see similar patterns like:

• اشتريت هذا من السوق = I bought this from the market
• أخذت الكتاب من المكتبة = I took the book from the library

ملابس means clothes/clothing and is a broken plural.

Its singular is traditionally مِلبَس or something related to a garment/article of clothing, but in actual modern usage, ملابس is the common word learners will meet for clothes.

Because it is a non-human plural, it affects adjective agreement in an important way.

This is one of the most important grammar points in Arabic:

Non-human plurals are usually treated grammatically like feminine singular when adjectives describe them.

So:

• ملابس = clothes
• جديدة = new

Together:

• ملابس جديدة = new clothes

Even though ملابس is plural in meaning, the adjective takes the feminine singular form.

This is standard in MSA:

• كتب جديدة = new books
• بيوت كبيرة = big houses
• سيارات سريعة = fast cars

Because possession automatically makes a noun definite in Arabic.

• مظلتي = my umbrella → definite, because it is specifically my umbrella

But:

• ملابس جديدة = new clothes → indefinite, because they are not specified as the new clothes

If the clothes were definite, you would expect something like:

• الملابس الجديدة = the new clothes

So the sentence contrasts a specific possessed object (my umbrella) with unspecified items bought later (new clothes).

Because they are definite nouns:

• الحافلة = the bus
• المتجر = the store

In the sentence, the speaker means a specific bus and a specific store, so the definite article الـ is used.

Also, the adjective must match definiteness when there is one. For example:

• ملابس جديدة = new clothes
• الملابس الجديدة = the new clothes

In these two words, the l of الـ is pronounced normally, because ح and م are moon letters, not sun letters.

So you pronounce:

• الحافلة = al-ḥāfila
• المتجر = al-matjar

Compare that with a sun-letter word like الشمس, where the l is not pronounced separately:

• الشمس = ash-shams

But here, with الحافلة and المتجر, the al- stays audible.

Yes. In normal Arabic writing, case endings and short vowels are usually omitted.

A fully vocalized version would look something like:

• اليومَ نسيتُ مظلتي في الحافلةِ، ولذلك اشتريتُ ملابسَ جديدةً من المتجرِ.

Some of the expected endings are:

• اليومَ as an adverb of time
• في الحافلةِ
• ملابسَ as the object of اشتريت
• جديدةً matching ملابس
• من المتجرِ

Learners often do not need to write these endings in everyday reading and writing, but it is useful to know they are there in formal grammar.

Yes.

Arabic allows some flexibility. For example:

• اليوم نسيت مظلتي في الحافلة...
• أنا نسيت مظلتي في الحافلة اليوم...

Both are understandable.

The original version sounds natural and neutral in MSA:

• time first: اليوم
• then the verb: نسيت
• then the object: مظلتي

Adding أنا gives extra emphasis, and moving اليوم changes the focus slightly. The original sentence is a very standard, smooth way to say it.