Πριν μπεις στο σπίτι, τίναξε λίγο τα αθλητικά σου, γιατί έχουν χώμα.

Because after πριν in this kind of sentence, Greek normally uses the subjunctive, not the indicative present.

So πριν μπεις means before you enter / before you go in.

Also, μπεις is based on the aorist form, which is very common here because the action is seen as a single complete event: entering once. Greek is focusing on aspect more than tense here.

So:

• πριν μπεις = before you enter
• not πριν μπαίνεις, which would not be the normal form here

Μπεις is the 2nd person singular aorist subjunctive of μπαίνω (to enter / go in).

Its subjunctive forms are:

• να μπω
• να μπεις
• να μπει
• να μπούμε
• να μπείτε
• να μπουν

In this sentence, the να is not expressed because after πριν, Greek often leaves it out.

So you can think of πριν μπεις as roughly before you enter, with μπεις meaning you enter in the subjunctive pattern.

Because in Modern Greek, πριν is very often followed directly by the subjunctive form without να.

So:

• πριν μπεις = very natural
• πριν να μπεις = also possible in some contexts, but less natural here

For learners, the safest thing is to get used to:

• πριν φύγω
• πριν έρθεις
• πριν μπεις

So the missing να is not a mistake. It is normal Greek.

Here it means into the house.

Greek uses σε + accusative after many verbs of motion, including μπαίνω. So:

• μπαίνω στο σπίτι = I go into the house / I enter the house

Also, στο is just the contraction of:

• σε + το = στο

So:

• στο σπίτι = into the house / in the house, depending on the verb
• with μπαίνω, the meaning is clearly into the house

Τίναξε is the aorist imperative of τινάζω.

Here it means something like:

• shake off
• shake out
• give ... a shake

In this sentence, it means shake your sneakers a bit so the dirt comes off.

The aorist imperative is used because this is a single, complete action:

• τίναξε = shake them once / do it now
• compare with τίναζε, which would sound more like a repeated or ongoing action

So τίναξε λίγο τα αθλητικά σου is a very natural way to say shake your sneakers a bit.

Λίγο literally means a little or a bit, but in commands it often softens the tone.

So here it does two things at once:

1. It means for a moment / a bit
2. It makes the command sound less abrupt

Compare:

• τίναξε τα αθλητικά σου = shake your sneakers
• τίναξε λίγο τα αθλητικά σου = shake your sneakers a bit

So λίγο is not only about quantity. It also makes the request sound more natural and less harsh.

Literally, αθλητικά is an adjective meaning athletic / sports-related, but in everyday Greek it is very commonly used as a noun to mean sports shoes, that is:

• sneakers
• trainers

So:

• τα αθλητικά = the sports shoes / sneakers
• τα αθλητικά σου = your sneakers

This is a very common kind of shorthand in Greek, where an adjective stands in for a noun that is understood.

Because Greek weak possessive forms like μου, σου, του, της usually come after the noun.

So Greek says:

• τα αθλητικά σου = your sneakers
• literally something like the sneakers your

This is normal Greek word order for these short possessive forms.

Compare:

• το βιβλίο μου = my book
• η φίλη σου = your friend
• τα κλειδιά του = his keys

So σου after the noun is exactly what you should expect.

Έχουν is plural because the subject is τα αθλητικά σου (your sneakers), which is plural.

So:

• τα αθλητικά σου έχουν χώμα = your sneakers have dirt on them

But χώμα is a mass noun, like dirt / soil, so it is normally singular here.

Greek is not saying they have a dirt or they have dirts. It is saying they have dirt on them.

Also, there is no article before χώμα because it is indefinite:

• έχουν χώμα = they have dirt
• not έχουν το χώμα, which would mean they have the dirt, a very different idea

Greek often leaves out words that are already understood from the context.

So after τίναξε λίγο τα αθλητικά σου, the listener already knows what have dirt refers to. That is why Greek can simply say:

• γιατί έχουν χώμα = because they have dirt

The subject is understood from what came just before.

You could say:

• γιατί τα αθλητικά σου έχουν χώμα

but it sounds more explicit and a little heavier. The shorter version is very natural in conversation.

Yes. The sentence is informal singular.

You can tell from:

• μπεις = you singular
• τίναξε = imperative singular
• σου = your, singular

So this is something you would say to one person that you address as εσύ.

If you were speaking to more than one person, or using the plural/polite form, the sentence would change accordingly.