Μόλις έρθεις σπίτι, βάλε τη ζύμη στο ψυγείο για την πίτα.

Here μόλις means as soon as.

So:

Μόλις έρθεις σπίτι, βάλε τη ζύμη στο ψυγείο
= As soon as you get home, put the dough in the fridge

Be careful: μόλις can also mean just in other contexts, for example Μόλις έφαγα = I just ate.
In this sentence, though, it introduces a time clause: as soon as...

Έρθεις is the form used after words like μόλις, όταν, αν, etc. when Greek is talking about a future or expected action.

It comes from the verb έρχομαι = I come / I am coming, but here Greek uses the subjunctive-type form:

• να έρθω = that I come
• να έρθεις = that you come

After μόλις, the να is not written, but the verb still appears in that form:

• Μόλις έρθεις... = As soon as you come / get home...

English uses a present form (as soon as you come home), but Greek uses this different verb form.

In natural English, it means As soon as you get home or As soon as you come home.

Greek uses σπίτι very naturally to mean home in many expressions, not just house as a physical building.

So:

• έρχομαι σπίτι = I come home
• είμαι σπίτι = I’m at home
• πάω σπίτι = I go home

Even though σπίτι literally means house/home, in this sentence the best English idea is home.

Because in Greek, some common expressions with σπίτι work without a preposition, especially when it means home in a general sense.

So Greek says:

• πάω σπίτι = I go home
• έρχομαι σπίτι = I come home
• μένω σπίτι = I stay home

This is similar to English, where we also say go home, not go to home.

If you were emphasizing a specific house, Greek could use other structures, but here σπίτι simply means home.

Βάλε is the singular imperative of βάζω = to put.

It means put!

So:

• βάλε = put! / place!
• βάλτε = put! when speaking to more than one person, or as a polite singular

Examples:

• Βάλε το βιβλίο εδώ. = Put the book here.
• Βάλτε τα πιάτα στο τραπέζι. = Put the plates on the table.

In your sentence, the speaker is giving one person an instruction: βάλε τη ζύμη στο ψυγείο = put the dough in the fridge

Because ζύμη is the direct object of the verb βάλε.

• η ζύμη = the dough as the subject
• τη(ν) ζύμη = the dough as the object

Compare:

• Η ζύμη είναι έτοιμη. = The dough is ready.
  Here η ζύμη is the subject.

• Βάλε τη ζύμη στο ψυγείο. = Put the dough in the fridge.
  Here τη ζύμη is the object.

So this is an accusative form.

Both are connected to the same article: την.

In modern Greek, την is often shortened to τη before certain consonants in everyday speech and writing.

So both of these can be seen:

• τη ζύμη
• την ζύμη

In most modern usage, τη ζύμη is very natural and common.

A quick guideline:

• before vowels or certain sounds, people often keep την
• before many consonants, τη is very common

So this is not a different article, just a shortened form.

Στο ψυγείο means in the fridge or into the fridge, depending on context.

It is made of:

• σε = in / to / at
• το = the

These combine into:

• σε το → στο

So:

• στο ψυγείο = in the fridge / into the fridge

With βάλε, English usually says put it in the fridge, so in the fridge is the natural translation.

This is a very common contraction in Greek.

The preposition σε combines with the definite article:

• σε + το = στο
• σε + τη(ν) = στη(ν)
• σε + τα = στα
• σε + τους = στους

Examples:

• στο σπίτι = at/to the house
• στην πόλη = in/to the city
• στα παιδιά = to the children

So στο ψυγείο is just the normal contracted form of σε το ψυγείο.

Yes, για την πίτα means for the pie.

It tells us what the dough is intended for:

τη ζύμη για την πίτα
= the dough for the pie

So the full sentence means something like:

As soon as you get home, put the dough for the pie in the fridge.

In English, we might also word it as:

• put the pie dough in the fridge
• put the dough for the pie in the fridge

Both give the right idea.

Most naturally, it goes with ζύμη:

• τη ζύμη για την πίτα = the dough for the pie

So it describes which dough we mean.

It does not usually mean something like put it in the fridge for the sake of the pie.
Instead, it identifies the dough as pie dough.

Greek often places this kind of phrase after the noun:

• το νερό για το τσάι = the water for the tea
• τα υλικά για το κέικ = the ingredients for the cake

Yes. Greek often puts the time clause first:

Μόλις έρθεις σπίτι, βάλε τη ζύμη στο ψυγείο.

This is very natural because it sets up when to do the action.

You could also rearrange it in conversation, for example:

Βάλε τη ζύμη στο ψυγείο μόλις έρθεις σπίτι.

That still means: Put the dough in the fridge as soon as you get home.

So the word order is flexible, but the original order is very normal and clear.

Yes, but the meaning changes slightly.

• μόλις έρθεις σπίτι = as soon as you get home
• όταν έρθεις σπίτι = when you get home

Μόλις emphasizes immediacy: do it right away after arriving.
Όταν is more general: when that happens, do this.

So in your sentence, μόλις suggests: the moment you get home, put the dough in the fridge

Here are the main dictionary forms:

• μόλις = as soon as / just
• έρθεις ← from έρχομαι = to come
• σπίτι = home / house
• βάλε ← from βάζω = to put
• ζύμη = dough
• ψυγείο = fridge / refrigerator
• πίτα = pie

This is useful because some forms in the sentence are not the dictionary forms:

• έρθεις is a conjugated verb form
• βάλε is an imperative
• τη / την is an article in the accusative

Then βάλε would become βάλτε.

So:

Μόλις έρθεις σπίτι, βάλτε τη ζύμη στο ψυγείο για την πίτα.

However, if you are being fully consistent, the verb in the first clause should also match the person you are addressing.

For you plural / polite you, you would normally say:

Μόλις έρθετε σπίτι, βάλτε τη ζύμη στο ψυγείο για την πίτα.

So:

• έρθεις / βάλε = singular informal
• έρθετε / βάλτε = plural or polite

It sounds like normal, everyday Greek.

Nothing in it is especially formal or literary.
It is the kind of sentence you might hear in a kitchen, at home, or in casual instructions.

A native speaker might say it exactly like this in ordinary life: Μόλις έρθεις σπίτι, βάλε τη ζύμη στο ψυγείο για την πίτα.