Το να μιλάω ελληνικά κάθε μέρα είναι η καλύτερη εξάσκηση.

It is a way of turning a verb phrase into a noun-like idea.

So το να μιλάω ελληνικά κάθε μέρα functions like a subject, similar to English speaking Greek every day.

Modern Greek does not use an infinitive the way English does, so instead of something like to speak, Greek often uses να + verb, and with το in front, the whole thing can act like a noun phrase.

In this sentence, το να μιλάω ελληνικά κάθε μέρα is the subject of είναι.

The το is what helps make the whole να-clause into a noun-like unit.

Without το, να μιλάω ελληνικά κάθε μέρα would not work well here as the subject of the sentence. It would sound more like a dependent clause, or in other contexts even like a wish, suggestion, or command.

So:

• να μιλάω... = just a να-clause
• το να μιλάω... = the act/idea of speaking...

This is about aspect.

• να μιλάω = imperfective aspect, used for repeated, habitual, or ongoing action
• να μιλήσω = perfective aspect, used for a single complete action

Because the sentence includes κάθε μέρα (every day), the action is clearly habitual and repeated. So να μιλάω is the natural choice.

Using να μιλήσω here would suggest more of a one-time event, which does not fit well with every day.

After να, it is better to think in terms of aspect rather than normal tense labels.

The form μιλάω here looks like the present, but after να it is part of the dependent system of the language. In practical learner terms, you can think of it as the imperfective form after να.

That is why it is used for something habitual like speaking Greek every day.

Not exactly.

English to speak is an infinitive. Modern Greek does not really have that kind of infinitive in everyday grammar. Instead, Greek usually uses να + finite verb form.

So in many translations, να may correspond to English to, but grammatically they are not the same thing.

For example:

• θέλω να μιλάω = I want to speak / I want to be speaking
• literally, Greek is not using an infinitive here

Both are correct forms of the same verb.

• μιλάω is very common in everyday speech
• μιλώ is also correct, but can sound a bit more formal or slightly more concise

So this sentence could also be written as:

Το να μιλώ ελληνικά κάθε μέρα είναι η καλύτερη εξάσκηση.

But μιλάω is probably the more natural choice for many speakers in ordinary conversation.

After verbs like μιλάω, names of languages are very often used without the article.

So Greek commonly says:

• μιλάω ελληνικά
• μιλάω αγγλικά
• μιλάω γαλλικά

This is the most neutral and natural pattern.

You may sometimes hear language names with the article in other contexts, but here the article-free form is exactly what you would expect.

Language names in Greek often appear in a neuter plural form, especially in expressions like speak Greek, learn Greek, and so on.

So:

• τα ελληνικά = the Greek language / Greek
• μιλάω ελληνικά = I speak Greek

This is just the normal way the language works; it does not mean Greeks or Greek things here.

Κάθε μέρα means every day.

After κάθε, Greek normally uses the singular:

• κάθε μέρα = every day
• κάθε εβδομάδα = every week
• κάθε χρόνο = every year

So the singular μέρα is exactly what you should expect.

Greek could also express a similar idea with καθημερινά, which is an adverb meaning daily or on a daily basis.

Because the subject is the whole clause Το να μιλάω ελληνικά κάθε μέρα, and that whole idea is treated as one thing.

Even though the clause contains several words, grammatically it functions as a single subject, so singular είναι is correct.

Compare the English idea:

• Speaking Greek every day is...

That is also singular in English.

There are two useful things to notice here.

First, καλύτερη is the form that agrees with εξάσκηση, which is:

• feminine
• singular
• nominative

So the adjective must match:

• η καλύτερη εξάσκηση

Second, Greek very commonly uses the definite article with superlatives:

• ο καλύτερος = the best
• η καλύτερη = the best
• το καλύτερο = the best

So η καλύτερη εξάσκηση means the best practice.

Because καλύτερος / καλύτερη / καλύτερο is the irregular comparative form of καλός.

So:

• καλός = good
• καλύτερος = better / best, depending on context

In this sentence, because of the article η, η καλύτερη is understood as the best.

Greek often uses this comparative form with the article to express the superlative idea.

It is nominative singular feminine.

That is because it is the predicate noun after είναι:

• subject: Το να μιλάω ελληνικά κάθε μέρα
• predicate: η καλύτερη εξάσκηση

In Greek, after είμαι, the predicate noun is normally in the nominative.

Sometimes yes, but εξάσκηση is especially natural here.

• άσκηση can mean exercise, drill, or practice
• εξάσκηση emphasizes practice in the sense of improving a skill through repeated use

Since the sentence is about building ability by speaking every day, εξάσκηση fits very well.

Yes, Greek word order is fairly flexible.

This sentence has a very natural, neutral order:

Το να μιλάω ελληνικά κάθε μέρα είναι η καλύτερη εξάσκηση.

You could move some parts for emphasis, for example:

Το να μιλάω κάθε μέρα ελληνικά είναι η καλύτερη εξάσκηση.

That is still understandable, but the original version sounds more natural to many speakers.

So yes, the order can change, but the given sentence is a very good standard model to learn from.