Kız arkadaşım yazın genellikle etek giyiyor, ama ben şortla daha rahat ediyorum.

It can mean either one depending on context, but in modern everyday Turkish, kız arkadaşım very often means my girlfriend.

Literally:

• kız = girl
• arkadaşım = my friend

So the phrase is literally my girl friend, but Turkish uses it idiomatically.

If someone wants to avoid ambiguity and clearly mean a non-romantic female friend, they might choose a different wording depending on context.

Because Turkish usually shows possession with a suffix on the noun instead of a separate word like my.

Here:

• arkadaş = friend
• arkadaşım = my friend

The -ım suffix means my.

So:

• kız arkadaşım = my girlfriend / my female friend

Turkish does have the separate word benim for my/mine, but it is often unnecessary:

• (Benim) kız arkadaşım = my girlfriend

The version without benim is completely normal.

Yazın means in summer or during the summer.

• yaz = summer
• yazın = in summer

This is a common time expression in Turkish. You will also see:

• kışın = in winter
• baharda = in spring
• sonbaharda = in autumn

So in this sentence, yazın tells you when the action usually happens.

Genellikle means generally or usually.

In this sentence:

• yazın genellikle etek giyiyor = she usually wears skirts in summer

Its position is fairly flexible, but it often appears before the verb or before the phrase it modifies.

For example, these are all natural:

• Kız arkadaşım yazın genellikle etek giyiyor.
• Kız arkadaşım genellikle yazın etek giyiyor.
• Genellikle kız arkadaşım yazın etek giyiyor.
  This one changes the emphasis a bit.

Good question. In Turkish, both forms can be used, but they feel slightly different.

• giyiyor = present continuous
• giyer = aorist / habitual-generic present

In everyday Turkish, the present continuous is very often used for regular habits too, especially in speech:

• Kız arkadaşım yazın genellikle etek giyiyor.
  = My girlfriend usually wears skirts in summer.

You could also say:

• Kız arkadaşım yazın genellikle etek giyer.

That also works, and it may sound a little more generally habitual or neutral.

So giyiyor here is completely natural.

Turkish often uses a bare singular noun to express a general category.

So:

• etek giyiyor can mean she wears skirts in a general sense

It does not have to mean only one skirt.

This is very common in Turkish:

• kitap okur = reads books
• kahve içer = drinks coffee
• etek giyiyor = wears skirts

Using etekler would sound more like specific skirts, not the general idea of skirt-wearing.

Şortla is şort + -la.

The suffix -la / -le often means:

• with
• using
• sometimes something like in / while wearing, depending on context

So:

• şortla daha rahat ediyorum literally means something like I am more comfortable with shorts
• In natural English here, it means I feel more comfortable in shorts or when I wear shorts

This is a very natural Turkish way to express comfort related to clothing.

Because rahat etmek is a very common Turkish expression meaning:

• to be comfortable
• to feel comfortable
• to be at ease

So:

• daha rahat ediyorum = I feel more comfortable
• daha rahatım = I am more comfortable

Both are possible, but rahat etmek is especially common when talking about comfort in a situation, activity, or clothing choice.

Here, şortla daha rahat ediyorum sounds very natural because the speaker is talking about how they feel when wearing shorts.

Yes, the verb ending already tells us the subject is I:

• ediyorum = I do / I am doing

So technically ben is not necessary.

However, Turkish often includes the pronoun for contrast or emphasis.

Here:

• ama ben... = but I...

That ben helps create a clear contrast:

• My girlfriend usually wears skirts in summer,
• but I feel more comfortable in shorts.

So it is there for emphasis, not because the grammar requires it.

Ama means but.

It connects the two contrasting ideas:

• Kız arkadaşım yazın genellikle etek giyiyor
• ama ben şortla daha rahat ediyorum

So the contrast is:

• she prefers skirts
• I feel more comfortable in shorts

It is one of the most common Turkish conjunctions.

Turkish word order is flexible, but the verb often comes near the end.

This sentence has a very natural structure:

• Kız arkadaşım = subject
• yazın = time
• genellikle = adverb
• etek = object/general noun
• giyiyor = verb

Then:

• ama = but
• ben = subject for contrast
• şortla = with/in shorts
• daha rahat = more comfortable
• ediyorum = verb

You could rearrange parts for emphasis, for example:

• Yazın kız arkadaşım genellikle etek giyiyor, ama ben şortla daha rahat ediyorum.

That still sounds natural. But keeping the verbs near the end is the safest pattern for learners.