Nếu trời mưa, giày của bạn sẽ bị ướt.

Nếu means if. It introduces a condition.

So:

• Nếu trời mưa = If it rains
• giày của bạn sẽ bị ướt = your shoes will get wet

This is a very common Vietnamese pattern:

Nếu + condition, result

Yes, trời can mean sky or heaven, but in weather expressions it often works like the weather/the sky.

So trời mưa is the normal way to say:

• it is raining
• it rains

Vietnamese does not need a dummy subject like English it in it rains.
So instead of a literal English-style structure, Vietnamese uses a weather expression:

• trời mưa = rain happens / the weather is rainy

This is completely natural Vietnamese.

No, you do not have to use thì, but you can.

All of these are natural:

• Nếu trời mưa, giày của bạn sẽ bị ướt.
• Nếu trời mưa, thì giày của bạn sẽ bị ướt.

Adding thì is a bit like saying then in English:

• If it rains, then your shoes will get wet.

It helps mark the result clause, but it is often omitted in everyday Vietnamese.

Giày của bạn means your shoes.

Breakdown:

• giày = shoes / footwear
• của = of
• bạn = you / your

So literally it is something like shoes of you.

This is a standard way to show possession in Vietnamese:

noun + của + possessor

Examples:

• nhà của tôi = my house
• xe của anh ấy = his car
• giày của bạn = your shoes

Yes, very often you can.

In everyday Vietnamese, của is frequently omitted when the possessor is a pronoun and the meaning is clear.

So both of these can work:

• giày của bạn
• giày bạn

The version with của can sound a little more explicit or careful.
The version without của often sounds more conversational.

Vietnamese nouns usually do not change form for singular or plural.

So giày can mean:

• shoe
• shoes
• footwear

The exact meaning comes from context.

In this sentence, English naturally uses shoes, so that is the best translation. Vietnamese does not need a separate plural ending like English -s.

If a speaker really wants to make plurality clearer, they can add words like:

• những
• các

But in this sentence that would usually be unnecessary.

Sẽ marks the future.

So:

• sẽ bị ướt = will get wet / will be wet

It is similar to English will.

However, Vietnamese often omits future markers if the time is already clear from context. So you may also hear:

• Nếu trời mưa, giày của bạn bị ướt.
• Nếu trời mưa, giày của bạn ướt.

Those can still be understood, but sẽ makes the future result more explicit.

Bị often marks that something happens to someone or something, especially when the result is unwanted, negative, or accidental.

Here:

• bị ướt = get wet / end up wet

So giày của bạn sẽ bị ướt suggests your shoes will be affected in an undesirable way.

This is not exactly the same as the English passive, even though it can sometimes look similar in translation.
It often adds the feeling of undergoing something unfortunate.

Both are natural, but the nuance is slightly different.

• giày của bạn sẽ ướt = your shoes will be wet
• giày của bạn sẽ bị ướt = your shoes will get wet / will end up wet

The version with bị emphasizes that the shoes are being affected by something, and that this is probably not desirable.

So:

• sẽ ướt = more neutral
• sẽ bị ướt = more affected/unfortunate

In many situations, either one would be understood perfectly well.

Vietnamese usually does not need a copula like English to be before many adjectives.

So:

• giày ướt literally looks like shoes wet
• but it means the shoes are wet

In Vietnamese, words like ướt can function like stative predicates.
That is why you do not need a separate word for are in this sentence.

This is very common:

• Tôi mệt. = I am tired.
• Nó cao. = He/She is tall.
• Giày ướt. = The shoes are wet.

Yes.

You can say:

• Nếu trời mưa, giày của bạn sẽ bị ướt.
• Giày của bạn sẽ bị ướt nếu trời mưa.

Both are grammatical and natural.

The first version is often a little easier for learners because it follows the clear pattern:

If X, Y

The second version is also common, especially when the speaker wants to emphasize the result first.

The comma is standard and helpful when the condition clause comes first:

• Nếu trời mưa, giày của bạn sẽ bị ướt.

In informal writing, people may sometimes leave it out, but using the comma is a good habit. It makes the sentence easier to read.

Yes, it is natural and correct.

Some very natural alternatives are:

• Nếu trời mưa, giày của bạn sẽ ướt.
• Nếu trời mưa, giày bạn sẽ ướt.
• Nếu trời mưa, thì giày của bạn sẽ bị ướt.

The original sentence is perfectly fine.
The main choice is whether you want the nuance of bị and whether you want the more explicit possession marker của.