Hindi lang bagay kay Liza ang berdeng palda, kundi komportable rin itong isuot sa paglalakad.

This is the Filipino pattern for not only ... but also.

• hindi lang = not only / not just
• kundi = but rather / but
• rin = also (same meaning as din)

So the sentence is structured like:

Hindi lang X, kundi Y rin
= Not only X, but Y also

This is a very common pattern in Filipino.

Because predicate-first word order is very common in Filipino.

In English, we usually start with the subject:
The green skirt suits Liza.

In Filipino, a very natural order is:
Bagay kay Liza ang berdeng palda.

Here:

• bagay kay Liza is the predicate
• ang berdeng palda is the ang-marked topic/subject-like element

You could also say:

Ang berdeng palda ay hindi lang bagay kay Liza, kundi komportable rin itong isuot sa paglalakad.

That version is grammatical too, but the original predicate-first order sounds very natural.

Here, bagay means to suit, to look good on, or to be appropriate for.

So:

Bagay kay Liza ang berdeng palda
means
The green skirt suits Liza
or
The green skirt looks good on Liza.

Be careful: bagay can also mean thing/object in other contexts. In this sentence, though, it is clearly the suit/look good on meaning.

Because after bagay, the person who is being suited is marked with kay if it is a singular personal name.

So:

• bagay kay Liza = suits Liza
• bagay kay Marco
• bagay kay Ana

Very roughly, kay here works a bit like to/for in English, though it does not translate word-for-word.

Why not the others?

• si Liza is used for a personal name in the topic/subject role
• ni Liza often marks an actor or possessor in other constructions
• kay Liza is the correct marker in this pattern

Because Filipino uses a linker between a modifier and the word it modifies.

Here, berde ends in a vowel, so it takes the linker -ng:

• berde + -ng + palda → berdeng palda

This is the normal way to say green skirt.

A few similar examples:

• magandang bahay = beautiful house
• malaking aso = big dog
• pulang kotse = red car

If the first word ends in a consonant, the linker is usually na instead.

Not exactly.

In this sentence, kundi is the normal word used in the fixed pattern:

hindi lang ... kundi ... rin
= not only ... but also

So kundi is the best choice here.

Pero means but, but it is more general. It does not fit this pattern as naturally.
So while pero and kundi can both connect contrasting ideas in some situations, here kundi is the standard and idiomatic choice.

Also, kundi is different from kung hindi:

• kundi = a conjunction like but rather / but
• kung hindi = literally if not

Rin and din mean the same thing: also / too.

The choice is mostly based on the sound of the word before it:

• Use rin after words ending in a vowel, w, or y
• Use din after most other sounds

Here the previous word is komportable, which ends in a vowel, so rin is the natural choice:

komportable rin

You may still hear variation in casual speech, but this is the standard guideline learners are usually taught.

Itong refers back to ang berdeng palda.

It is made of:

• ito = this / it
• -ng = linker

So itong isuot literally looks like this/it to wear.

In natural English, that becomes it to wear or more smoothly comfortable to wear.

Why not just ito? Because in this structure, the pronoun is linked to the following word:

• madali itong gawin = it is easy to do
• mahirap itong intindihin = it is hard to understand
• komportable itong isuot = it is comfortable to wear

So itong is the normal form before isuot.

Isuot is a verb meaning to wear / to put on.

In komportable rin itong isuot, it means it is also comfortable to wear.

This is a natural choice because the focus is on the thing being worn—the skirt. The sentence is talking about the skirt as an item of clothing and saying that it is comfortable to wear.

Learners often compare this with magsuot:

• magsuot focuses more on the person doing the wearing
• isuot works well when the clothing item itself is central

So in this sentence, isuot fits very well.

Sa paglalakad means while walking, when walking, or for walking, depending on context.

Here it means something like:

• comfortable to wear while walking
• comfortable to wear on walks

Paglalakad is a verbal noun or gerund-like form from lakad (walk).

Formation:

• root: lakad
• noun/action form: paglalakad

So paglalakad means walking or the act of walking.

This kind of pag- form is very common in Filipino.

Filipino often uses a pronoun instead of repeating the full noun phrase.

So instead of saying something like:

... kundi komportable rin ang berdeng palda na isuot ...

the sentence naturally uses itong to refer back to the skirt:

... kundi komportable rin itong isuot ...

This avoids repetition and sounds smoother. English does the same kind of thing with it:

The green skirt not only suits Liza, but it is also comfortable to wear.

No hidden ay is required. The sentence is already complete and natural as it is.

Filipino often has two common ways to build this kind of sentence:

1. Predicate-first
   Hindi lang bagay kay Liza ang berdeng palda...

2. Topic-first with ay
   Ang berdeng palda ay hindi lang bagay kay Liza...

Both are grammatical. The original sentence simply uses the very common predicate-first pattern, so no ay is needed.