Η πλάκα ήταν καλή.

Η is the feminine singular definite article, so it means the.

In Greek, the changes form depending on gender, number, and case. Here, πλάκα is a feminine singular noun, so the correct article is η.

So:

• η = the for a feminine singular noun in the nominative case

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

One clue is its ending: many feminine nouns end in -α or -η, although this is not a perfect rule in every case.

Because πλάκα is feminine, other words connected to it must match it, such as:

• the article: η
• the adjective: καλή

This matching is called agreement.

Because adjectives in Greek must agree with the noun they describe in gender, number, and case.

Since πλάκα is:

• feminine
• singular
• nominative

the adjective must also be feminine singular nominative:

• καλός = masculine
• καλή = feminine
• καλό = neuter

So Η πλάκα ήταν καλή is correct because καλή matches πλάκα.

Ήταν is the past tense form of είμαι (to be).

In this sentence, it means was.

So:

• είναι = is
• ήταν = was / were

Greek uses ήταν for several persons, so it can mean:

• I was
• you were
• he/she/it was
• they were

The exact meaning depends on the context.

Because Greek often does not need an extra subject pronoun when the subject is already clear.

In Η πλάκα ήταν καλή, the subject is η πλάκα, so there is no need to add a separate word for it.

English often says:

• It was good

But Greek can directly say:

• Η πλάκα ήταν καλή
• literally: The joke/fun was good

Greek commonly avoids unnecessary pronouns.

Not always. Πλάκα is a very common Greek word with several meanings depending on context.

It can mean things like:

• joke
• fun
• teasing
• messing around
• even more literal meanings in other contexts, such as a slab or plate

So in a sentence like Η πλάκα ήταν καλή, the intended meaning depends on the situation. It might mean something like:

• The joke was good
• The fun was good
• The teasing was good

This is a good example of a word whose meaning is very context-dependent.

Greek uses accent marks to show which syllable is stressed.

In this sentence:

• Η — no written accent, pronounced i
• πλάκα — stress on πλά
• ήταν — stress on ή
• καλή — stress on λή

So the rhythm is roughly:

• i PLA-ka I-tan ka-LI

The accent mark is very important in Greek spelling and pronunciation.

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

The neutral order here is:

• Η πλάκα ήταν καλή.

But you could also hear:

• Καλή ήταν η πλάκα.

This still means the same basic thing, but the emphasis changes a little.
For example, Καλή ήταν η πλάκα can sound more like:

• The joke was good
• or The joke was good, actually

So Greek word order can shift for focus or emphasis.

Because after the verb είμαι (to be), the adjective describing the subject agrees with the subject.

Here:

• η πλάκα = the subject
• καλή = adjective describing the subject

Since the adjective refers back to the subject, it stays in the nominative, matching the noun.

So this is different from some other structures where Greek changes case.
With to be, the describing adjective matches the subject directly.

You add δεν before the verb:

• Η πλάκα δεν ήταν καλή.
• The joke/fun was not good.

That is the normal way to negate a sentence with ήταν.

Pattern:

• ήταν = was
• δεν ήταν = was not

Yes. In everyday speech, some speakers also use ήτανε.

So you may hear:

• Η πλάκα ήταν καλή.
• Η πλάκα ήτανε καλή.

Both are understood, and both are common.
Ήταν is the standard written form you should definitely know first.

You would change ήταν to είναι:

• Η πλάκα είναι καλή.
• The joke/fun is good.

So the pattern is:

• είναι = is
• ήταν = was

This is a very useful pair to learn early.