Sân vận động rất lớn.

In Vietnamese, you usually do not need a verb like to be when you are simply describing something with an adjective.

So:

• Sân vận động rất lớn = The stadium is very big

The structure is basically:

• noun + degree word + adjective

Here:

• sân vận động = stadium
• rất = very
• lớn = big/large

So Vietnamese often says the equivalent of stadium very big, and that already means the stadium is very big.

A helpful breakdown is:

• sân = yard, field, court
• vận động = physical activity, sports, exercise
• sân vận động = stadium
• rất = very
• lớn = big, large

So sân vận động is a fixed expression meaning stadium, even though its parts have their own meanings.

Vietnamese word order is different from English.

In this sentence, lớn is part of the predicate, so the pattern is:

• subject + adjective
• Sân vận động rất lớn = The stadium is very big

Also, when an adjective directly modifies a noun in Vietnamese, it usually comes after the noun too:

• sân vận động lớn = a big stadium

So Vietnamese commonly places adjectives after nouns, unlike English.

Rất means very and intensifies the adjective.

• Sân vận động lớn = The stadium is big
• Sân vận động rất lớn = The stadium is very big

Yes, you can leave it out if you just want to say big rather than very big.

It is one vocabulary item in meaning, but it is written as multiple syllables.

Vietnamese writing usually separates syllables with spaces, so many multi-syllable words look like several written units.

So:

• sân vận động is one expression meaning stadium
• even though it is written with spaces

This is very normal in Vietnamese.

A simple learner-friendly guide is:

• sân: roughly like suhn, with a flat/level tone
• vận: roughly vuhn, with a heavy low tone
• động: roughly dong/dohng, also with a heavy low tone
• rất: roughly zut or rut depending on dialect, with a rising tone
• lớn: roughly lurn or luhn, with a rising tone

A few useful notes:

• đ is pronounced like English d
• the letter ơ/ớ in lớn is a vowel English does not have exactly
• tones matter a lot in Vietnamese

If you are learning pronunciation, it is best to listen to native audio, because Vietnamese tones and vowels are hard to master from English spelling alone.

Vietnamese does not use articles the same way English does.

So a bare noun like sân vận động can mean:

• a stadium
• the stadium
• sometimes just stadiums in a general sense

The exact meaning depends on context.

If you want to be more specific, you can add words such as:

• một sân vận động = a stadium
• sân vận động này = this stadium
• sân vận động đó = that stadium

No. Lớn is very common and natural, but Vietnamese also has to, which can also mean big.

For example:

• Sân vận động rất lớn
• Sân vận động rất to

Both can work. In many situations, they are close in meaning.

Very roughly:

• lớn often feels broader and very standard
• to often emphasizes physical size a bit more

For a beginner, lớn is an excellent and safe choice.

Yes. Sân vận động rất lớn is a complete and natural sentence.

It has:

• a subject: sân vận động
• a predicate: rất lớn

Vietnamese does not need extra words to make this sentence complete. It is perfectly normal as a simple description.

You can add a demonstrative:

• Sân vận động này rất lớn = This stadium is very big
• Sân vận động đó rất lớn = That stadium is very big

So:

• này = this
• đó/kia = that

These usually come after the noun in Vietnamese, not before it.