La stoffa di questa camicia è molto leggera.

Because stoffa is a feminine singular noun in Italian, so it takes the feminine singular definite article la.

• la stoffa = the fabric
• il tessuto = the fabric/textile (different word, masculine)

In Italian, you usually have to learn each noun together with its gender:

• la camicia = shirt
• la stoffa = fabric

Di questa camicia means of this shirt and tells you which fabric you are talking about.

So the structure is:

• La stoffa = the fabric
• di questa camicia = of this shirt

Together:

• La stoffa di questa camicia = The fabric of this shirt

Italian often uses di where English might prefer of or sometimes a possessive structure.

Because camicia is a feminine singular noun, and the demonstrative must agree with it.

So:

• questa camicia = this shirt
• questo libro = this book

Agreement matters in Italian:

• masculine singular: questo
• feminine singular: questa
• masculine plural: questi
• feminine plural: queste

Because leggera describes la stoffa, not la camicia directly, and stoffa is feminine singular.

Italian adjectives usually agree in gender and number with the noun they describe.

• la stoffa è leggera = the fabric is light
• il tessuto è leggero = the fabric/material is light

Even though camicia is also feminine, the adjective is agreeing with the subject stoffa.

Here molto is being used as an adverb, meaning very, so it does not change form.

• molto leggera = very light
• molto bella = very beautiful
• molto interessante = very interesting

But when molto is an adjective meaning much/many, it does agree:

• molta stoffa = a lot of fabric
• molti libri = many books

So in this sentence:

• molto = very → no agreement needed

È is the third-person singular of essere (to be), because the subject is singular:

• La stoffa ... è ... = The fabric ... is ...

This is a basic pattern in Italian:

• Il libro è interessante.
• La casa è grande.
• La stoffa è molto leggera.

Also note the accent:

• è = is
• e = and

That accent is important in writing.

Yes, absolutely. That is also correct.

The difference is mainly vocabulary:

• stoffa often means fabric/cloth
• tessuto can also mean fabric/textile/material

If you use tessuto, the adjective must change because tessuto is masculine:

• Il tessuto di questa camicia è molto leggero.

Compare:

• La stoffa ... è molto leggera.
• Il tessuto ... è molto leggero.

In this sentence, leggera is not directly placed next to the noun because it comes after essere as a predicate adjective:

• La stoffa è leggera = The fabric is light

This is similar to English:

• The fabric is light

Italian can place adjectives after nouns in many cases, but here the key point is that leggera comes after the verb è, so it is simply describing the subject through the verb.

Normally, no. In standard Italian, you would say:

• La stoffa di questa camicia è molto leggera.

Italian uses definite articles more often than English does, and in this sentence the article sounds natural and expected.

Without la, the sentence would sound incomplete or unnatural in standard usage.

Usually camicia means shirt. Depending on context, it can refer to:

• a men’s shirt
• a women’s blouse/shirt

So the exact English translation may vary slightly by context, but grammatically it is still a feminine noun:

• la camicia

That is why you get:

• questa camicia
• la camicia è nuova

If you wanted to say The fabric of these shirts is very light, you would change the demonstrative and the noun camicia to the plural:

• La stoffa di queste camicie è molto leggera.

Why?

• questa camicia → queste camicie
• stoffa stays singular if you are still talking about the fabric as one general thing
• è molto leggera stays singular because the subject is still la stoffa

But if the subject itself became plural, then the verb and adjective would also change.

For example:

• Le stoffe di queste camicie sono molto leggere.
• The fabrics of these shirts are very light.