أنا لا أستطيع أن أمشي اليوم، لكن صديقتي تمشي إلى الحديقة في المساء.

Yes. أستطيع already tells you the subject is I because of the prefix أ-.

So أنا is not strictly necessary here. You could say:

لا أستطيع أن أمشي اليوم

and it would still mean I can’t walk today.

Including أنا can add:

• clarity
• emphasis
• a more explicit contrast with صديقتي later in the sentence

So أنا لا أستطيع... لكن صديقتي... feels a bit like As for me, I can’t..., but my friend...

In Modern Standard Arabic, لا is the normal way to negate an imperfect/present verb.

So:

• أستطيع = I can / I am able
• لا أستطيع = I cannot / I am not able

A native English speaker may wonder whether Arabic uses something like not after the verb, but in Arabic the negative usually comes before the verb.

After verbs like أستطيع (I can / I am able), Arabic usually uses:

أن + imperfect verb

So:

• أستطيع أن أمشي = literally I am able that I walk
• natural English: I can walk

This is one of the big differences from English: Arabic does not usually use an infinitive like to walk in the same way English does. Instead, it often uses أن plus a conjugated verb.

Grammatically, it does change: after أن, the imperfect verb is normally in the subjunctive.

In fully vowelled Arabic:

• indicative: أمشي
• subjunctive after أن: أمشيَ

But in normal everyday writing without full vowels, both are usually written the same way:

أمشي

So the learner often cannot see the change, even though the grammar is different.

Both come from the same verb, مشى / يمشي (to walk).

The difference is the subject:

• أمشي = I walk
• تمشي = she walks

In the imperfect tense, the prefix tells you the person/gender:

• أ- = I
• ت- = she (and also you in some forms, depending on context)

So:

• أن أمشي = that I walk
• صديقتي تمشي = my female friend walks

The base word is:

صديقة = a female friend

When you add -ي (my), it becomes:

صديقتي = my female friend

The final ة (called tāʾ marbūṭa) often sounds like -a / -ah when the word stands alone, but when a suffix is added, the underlying t shows up:

• صديقة
• صديقتي

So this is completely normal. The same thing happens in many feminine nouns.

In Arabic, possession is often shown by attaching a suffix pronoun directly to the noun.

So:

• صديقة = female friend
• صديقتي = my female friend

The suffix -ي means my.

This is different from English, where my is a separate word. In Arabic, attached pronouns are extremely common:

• كتابي = my book
• بيتي = my house
• صديقتي = my female friend

Yes. Both لكن and ولكن can mean but.

• لكن is the shorter form
• ولكن is a slightly fuller form and often sounds a bit more formal or literary

In many contexts, both are fine. In this sentence, لكن is perfectly natural:

• ..., لكن صديقتي تمشي...

So a learner can think of لكن as a standard word for but.

إلى means to / toward and is commonly used for movement toward a destination.

So:

• تمشي إلى الحديقة = she walks to the park/garden

This is the normal preposition when someone moves toward a place.

Compare:

• إلى البيت = to the house
• إلى المدرسة = to the school
• إلى الحديقة = to the garden/park

حديقة means a garden / a park, while الحديقة means the garden / the park.

So:

• إلى حديقة = to a garden
• إلى الحديقة = to the garden / to the park

In this sentence, the place is presented as definite, so الـ is used.

Depending on context, English and Arabic do not always match perfectly in definiteness, but here الحديقة is the straightforward definite form.

This is a very common learner question.

اليوم often works by itself as an adverb of time:

• اليوم = today

So Arabic naturally says:

• أمشي اليوم
• لا أستطيع اليوم

You do not need في there.

But في المساء is a very common expression meaning in the evening.

So the sentence has:

• اليوم = today
• في المساء = in the evening

Arabic time expressions are not always built the same way. Some appear with no preposition, and some commonly use في.

This is the imperfect form, and Arabic imperfect verbs can cover several meanings that English separates.

Depending on context, تمشي can mean things like:

• she walks
• she is walking
• she will walk
• she goes walking

The surrounding context tells you which meaning is intended.

In this sentence, the time expression في المساء helps narrow it down. It could describe:

• a habitual action: she walks to the park in the evening
• or a planned action later today, depending on the broader situation

So the Arabic form itself is flexible, and the context does the extra work.

Yes, Arabic allows more than one word order.

The sentence as given uses:

• لكن صديقتي تمشي...

This puts صديقتي first, which helps make the contrast clear after لكن.

Arabic can also use verb-first order:

• لكن تمشي صديقتي إلى الحديقة...

That is grammatical, but it sounds a bit different in focus and style.

For learners, the given order is very useful because it clearly highlights:

• I cannot walk today
• but my friend walks to the park in the evening

So the noun-first order works well for contrast.

You would change both the noun and the verb agreement.

Instead of:

• صديقتي = my female friend
• تمشي = she walks

you would use:

• صديقي = my male friend
• يمشي = he walks

So the second half would become:

لكن صديقي يمشي إلى الحديقة في المساء

This is a good example of how Arabic marks gender more consistently than English does:

• the noun changes
• the verb also changes to match the subject