Όταν αντιμετωπίζεις πολλά μαζί, είναι βολικό να γράφεις πρώτα τα πιο σημαντικά σε ένα μικρό σημειωματάριο.

Yes, but it is a general you, just like English often uses you to mean anyone.

So Όταν αντιμετωπίζεις πολλά μαζί does not have to mean one specific person. It means something like when you are dealing with many things at once in a general, advice-giving way.

Greek often uses the 2nd person singular like this in everyday language:

• Αν θέλεις να μάθεις, διαβάζεις κάθε μέρα.
• Όταν βιάζεσαι, κάνεις λάθη.

In both cases, it means people in general, not only one specific you.

Όταν means when and introduces a time clause.

In this sentence, Όταν αντιμετωπίζεις πολλά μαζί sets the situation in which the advice applies.

A useful point: Greek often uses the present tense after όταν when talking about something habitual or generally true:

• Όταν κουράζεσαι, χρειάζεσαι ξεκούραση.
• Όταν έχεις πολλά, οργανώνεσαι καλύτερα.

So here, the idea is not one single event, but a recurring situation: whenever this happens.

πολλά is the neuter plural form of πολύς and here it means many things or a lot.

Greek often uses adjectives like this on their own, without an explicit noun, when the noun is understood:

• πολλά = many things / a lot
• λίγα = a few things / little
• σημαντικά = important things

μαζί means together, and in this context it means all at once.

So πολλά μαζί is literally something like many things together, which naturally means many things at the same time.

It is not agreeing with a noun here. This is an impersonal construction.

είναι βολικό means it is convenient / practical / useful. Greek very often uses a neuter singular adjective in this kind of impersonal statement:

• Είναι εύκολο να το κάνεις.
• Είναι δύσκολο να θυμάσαι τα πάντα.
• Είναι καλό να ξεκουράζεσαι.

So βολικό is neuter singular because Greek uses that form for general it is ... to ... statements.

Modern Greek does not use an infinitive the way English does.

Where English says to write, Greek usually uses να + verb:

• θέλω να γράψω = I want to write
• είναι καλό να κοιμάσαι νωρίς = it is good to sleep early

So in this sentence:

• είναι βολικό να γράφεις... = it is convenient to write...

This is one of the biggest structural differences between English and Greek.

This is about aspect, which is very important in Greek.

• να γράφεις = imperfective aspect
• να γράψεις = perfective aspect

Here, να γράφεις is used because the sentence is giving general advice or describing a habitual / repeated practice. It means something like to be writing / to write as a regular strategy.

If you said να γράψεις, it would sound more like write them down once, focusing on a single completed action.

So:

• να γράφεις = a general method or ongoing practice
• να γράψεις = one complete act

In this sentence, the imperfective fits better because the speaker is recommending a useful habit.

πρώτα is an adverb meaning first.

It tells you the order of the action: write the most important things first.

Greek adverb placement is often flexible, but this position is very natural:

• να γράφεις πρώτα τα πιο σημαντικά

This means:

1. identify the most important things
2. put those down before the others

So πρώτα modifies να γράφεις and gives the sense of priority.

τα πιο σημαντικά means the most important things.

Breakdown:

• τα = neuter plural definite article
• πιο = more
• σημαντικά = important, neuter plural

Greek often forms the superlative with:

• article + πιο + adjective

So:

• το πιο σημαντικό = the most important thing
• τα πιο σημαντικά = the most important things

Also, the noun is omitted. Greek is using the adjective as a noun:

• τα πιο σημαντικά = literally the most important ones / things

That is very common in Greek.

Yes. Both are possible.

• τα πιο σημαντικά = the most common and everyday way
• τα σημαντικότερα = also correct, a bit more compact and sometimes a little more formal in tone

Both mean the most important things.

So the sentence could also be phrased with τα σημαντικότερα, but τα πιο σημαντικά sounds very natural in modern everyday Greek.

After σε, Greek uses the accusative.

So:

• σε ένα μικρό σημειωματάριο

contains:

• ένα = accusative neuter singular article
• μικρό = accusative neuter singular adjective
• σημειωματάριο = accusative neuter singular noun

The whole phrase means in a small notebook.

The adjective and article agree with the noun:

• ένα μικρό σημειωματάριο
• all three are neuter singular accusative

σημειωματάριο is a neuter noun meaning notebook or notepad.

Its ending -ιο is very common for neuter nouns:

• βιβλίο
• σχολείο
• γραφείο
• σημειωματάριο

In this sentence, it is singular because the idea is a small notebook, not notebooks in general.

Greek often leaves out the equivalent of English it in impersonal expressions.

English says:

• It is useful to...
• It is easy to...

Greek simply says:

• Είναι χρήσιμο να...
• Είναι εύκολο να...
• Είναι βολικό να...

So the sentence does not need an explicit subject. The idea of it is built into the impersonal structure.

Greek word order is fairly flexible, although some orders sound more natural than others.

The given order is very natural:

• Όταν αντιμετωπίζεις πολλά μαζί, είναι βολικό να γράφεις πρώτα τα πιο σημαντικά σε ένα μικρό σημειωματάριο.

But parts of it could move for emphasis. For example:

• Όταν αντιμετωπίζεις πολλά μαζί, είναι βολικό να γράφεις σε ένα μικρό σημειωματάριο πρώτα τα πιο σημαντικά.

That is still understandable, but the original version flows better and sounds more natural.

So the word order is not completely fixed, but the original sentence is a good model for normal usage.