Το φορτίο είναι βαρύ.

A good rough pronunciation is:

to for-TEE-o EE-ne va-REE

More exactly:

• Το = to
• φορτίο = for-TEE-o
• είναι = EE-ne
• βαρύ = va-REE

The accent marks show where the stress goes:

• φορτίο
• είναι
• βαρύ

Το is the definite article, so it means the.

It is the form used with a neuter singular noun in the nominative (subject) or accusative case.

So:

• το φορτίο = the load / the cargo

In Greek, every noun has a grammatical gender: masculine, feminine, or neuter.

φορτίο happens to be a neuter noun. That does not mean the object itself is biologically neuter; it is just how the noun is classified in Greek grammar.

Because φορτίο is neuter singular:

• the article is το
• the adjective must also be in the neuter singular form

Because the adjective has to agree with the noun.

The basic dictionary form is often the masculine:

• βαρύς = heavy (masculine)

But here the noun φορτίο is neuter singular, so the adjective must also be neuter singular:

• masculine: βαρύς
• feminine: βαριά
• neuter: βαρύ

So:

• Το φορτίο είναι βαρύ. = The load is heavy.

είναι is the verb to be, here meaning is.

In this sentence:

• Το φορτίο = the subject
• είναι = is
• βαρύ = heavy

So the structure is very similar to English:

• The load is heavy.

A useful detail: είναι is also the form for they are, so Greek relies on context.

Because Greek often does not use subject pronouns unless they are needed for emphasis or clarity.

English usually says:

• It is heavy

But Greek can simply say:

• Είναι βαρύ = It is heavy

And if the noun is stated, as in your sentence, there is even less reason to add a pronoun:

• Το φορτίο είναι βαρύ

Yes. Greek word order is more flexible than English word order.

The neutral, straightforward order is:

• Το φορτίο είναι βαρύ.

But other orders are possible for emphasis, for example:

• Βαρύ είναι το φορτίο.
• Είναι βαρύ το φορτίο.

These do not usually change the basic meaning, but they can change the focus or emphasis.

Yes. In your sentence, βαρύ is a predicate adjective: it comes after είναι and describes the subject.

So:

• Το φορτίο είναι βαρύ. = The load is heavy.

If you want the adjective directly before the noun, like the heavy load, Greek does that too:

• το βαρύ φορτίο

So compare:

• το βαρύ φορτίο = the heavy load
• το φορτίο είναι βαρύ = the load is heavy

You add δεν before the verb:

• Το φορτίο δεν είναι βαρύ.

So:

• δεν = not
• είναι = is

This is the normal way to negate a sentence with είμαι.

The plural would be:

Τα φορτία είναι βαριά.
= The loads are heavy.

Notice that all the words change as needed:

• το → τα
• φορτίο → φορτία
• βαρύ → βαριά

Again, the adjective agrees with the noun in number and gender.

Greek does have an indefinite article, roughly equivalent to a/an:

• ένα φορτίο = a load

So:

• Ένα φορτίο είναι βαρύ. = A load is heavy.

But Greek often uses the definite article more widely than English, and sometimes it can also omit the article depending on context.

In this sentence:

• το φορτίο is in the nominative, because it is the subject
• βαρύ is also in the nominative, because it is a predicate adjective describing the subject after είναι

So even though English learners often focus first on meaning, the grammar is:

• subject: το φορτίο
• verb: είναι
• predicate adjective: βαρύ

That is why the adjective must match the subject grammatically.