Πριν βάλω το ράφι, ανέβηκα ένα σκαλοπάτι και κράτησα καλά το τρυπάνι.

After πριν (before), Greek usually uses the subjunctive / perfective non-past to refer to an action that is still pending relative to the main action. So πριν βάλω το ράφι means before I put up / install the shelf.

Why this form?

• βάλω presents the action as one complete act
• έβαλα is a normal past tense form
• βάζω would sound more ongoing, repeated, or less bounded

So βάλω is the natural choice here.

Not by itself. βάλω is the same form Greek uses in several structures. It can have future meaning only when something like θα is added:

• θα βάλω = I will put / install
• πριν βάλω = before I put / install

So in this sentence, βάλω is not a future tense by itself. It is the form Greek uses after πριν.

Yes. You can hear both:

• πριν βάλω
• πριν να βάλω

Both are natural. The version without να is very common in everyday Greek.

ανέβηκα is the aorist of ανεβαίνω (to go up / climb up).

The aorist shows the action as a single completed event in the past. So here it means something like:

• I stepped up
• I went up
• I climbed up

If Greek wanted to show an ongoing or repeated action, it would use the imperfect instead:

• ανέβαινα = I was going up / I used to go up

Because ένα σκαλοπάτι here expresses the amount of movement: one step.

So:

• ανέβηκα ένα σκαλοπάτι = I went up one step

Greek can use the accusative like this after verbs of motion.

Compare:

• ανέβηκα ένα σκαλοπάτι = I went up one step
• ανέβηκα στο σκαλοπάτι = I stepped onto the step

So the version in your sentence focuses on how far the speaker moved, not the exact surface they moved onto.

It can mean a single step / stair. In this sentence, ένα σκαλοπάτι means one step or one stair, depending on how you would naturally say it in English.

English often chooses whichever sounds more natural in context, but the Greek word itself can cover both.

καλά is an adverb, so it tells you how the speaker held the drill.

Literally, καλά often means well, but in this context the more natural English idea is:

• firmly
• securely
• carefully

So κράτησα καλά το τρυπάνι means the speaker held the drill firmly / securely.

Greek uses καλά in many places where English prefers a more specific adverb.

Because both ράφι (shelf) and τρυπάνι (drill) are neuter singular nouns.

In the neuter singular, the definite article is το in both:

• the nominative
• the accusative

Here both nouns are direct objects:

• βάλω το ράφι
• κράτησα το τρυπάνι

So το is exactly what you expect.

Because Greek often leaves out subject pronouns when they are not needed. The verb ending already shows the subject.

Here the verb forms already tell you it is I:

• βάλω
• ανέβηκα
• κράτησα

So Greek does not need εγώ here.

If you did say εγώ, it would usually add emphasis or contrast:

• Εγώ ανέβηκα... = I went up...

Greek βάζω is broader than English put. Depending on context, it can mean:

• put
• place
• set
• install
• put up

So with ράφι, the natural English meaning is often put up the shelf or install the shelf, even though Greek simply uses βάζω.

Because the sentence is narrating a sequence of completed past actions.

That is a very common use of the Greek aorist:

1. ανέβηκα ένα σκαλοπάτι
2. κράτησα καλά το τρυπάνι

The aorist is the normal tense for telling events like this. If the speaker wanted to show background action or something ongoing, Greek would more likely use the imperfect.

Yes. Greek word order is fairly flexible.

For example, you could also say:

• κράτησα το τρυπάνι καλά

The basic meaning stays the same, but the emphasis may shift slightly. Greek often moves adverbs and objects around more freely than English, because articles and verb endings already make the grammar clear.