Белый гриб съедобный.

In Russian, the verb to be is usually omitted in the present tense.

So:

Белый гриб съедобный.
literally looks like: White mushroom edible.

But it means: The white mushroom / porcini mushroom is edible.

If you wanted past or future, Russian would normally use a form of быть:

• Белый гриб был съедобным. = The porcini mushroom was edible.
• Белый гриб будет съедобным. = The porcini mushroom will be edible.

All three words are in the nominative singular masculine:

• белый — nominative singular masculine adjective
• гриб — nominative singular masculine noun
• съедобный — nominative singular masculine adjective

Белый гриб is the subject, and съедобный is the predicate adjective describing it.

Because they both agree with гриб, which is a masculine singular noun in the nominative case.

Russian adjectives change their endings to match the noun they describe or refer back to.

For example:

• белый гриб — masculine singular
• белая книга — feminine singular
• белое вино — neuter singular
• белые грибы — plural

The same agreement happens with съедобный in this sentence.

Literally, it means white mushroom, but in Russian белый гриб is also the normal name for a specific mushroom: porcini / cep / king bolete.

So depending on context, this is usually understood not as just any mushroom that is white in color, but as the specific kind called белый гриб.

Because here съедобный is not just another adjective inside the noun phrase. It is the predicate of the sentence.

Structure:

• Белый гриб = the subject
• съедобный = what is being said about the subject

So the meaning is:

The porcini mushroom is edible.

If you said:

съедобный белый гриб

that would be one noun phrase meaning:

an edible porcini mushroom
or
an edible white mushroom

So word order changes the structure, not just the style.

Yes. That is also correct.

• съедобный = full adjective form
• съедобен = short adjective form

Both can mean edible here.

Very roughly:

• съедобный sounds more neutral and descriptive
• съедобен sounds a bit more concise, formal, or dictionary-like

So both are natural, but съедобен is especially common in short factual statements like definitions or labels.

The hard sign separates the prefix с- from the following е.

It shows that the е is pronounced with a y-sound onset, roughly like ye, instead of simply softening the previous consonant.

So съедобный starts approximately like:

sye-DOB-nyy

The ъ does not have a sound of its own; it just affects pronunciation and spelling.

Russian has no articles like a and the, so the exact English choice depends on context.

This sentence could be interpreted in different ways in English, but because белый гриб is often a species name, it is commonly understood as something like:

• The porcini mushroom is edible
• Porcini is edible
• A porcini mushroom is edible

English has to choose an article; Russian usually does not.

There is no comma because this is just a simple sentence, not a list or a clause combination.

There is no dash because Russian usually uses a dash in present-tense sentences when the predicate is a noun, especially in clear equation-type statements:

• Москва — столица России. = Moscow is the capital of Russia.

But with an adjective predicate like съедобный, a dash is normally not used:

• Белый гриб съедобный.

The noun and adjectives would all change to plural:

• Белые грибы съедобны. = Porcini mushrooms are edible.

You may also hear:

• Белые грибы съедобные.

But in short factual statements, the short-form predicate съедобны is often especially natural.

The main thing to notice is agreement:

• белый гриб → белые грибы
• съедобный → съедобны or съедобные, depending on the form you choose