Streĉu la ŝraŭbon per la ŝraŭbturnilo.

The ending -u is the Esperanto command / request / jussive ending.

So:

• streĉi = to tighten / to make taut
• streĉu = tighten! / tighten it

This form is used for:

• commands: Fermu la pordon. = Close the door.
• requests: Atendu momenton. = Wait a moment.
• suggestions: Ni iru. = Let’s go.

So in this sentence, streĉu is telling someone to do the action.

Because ŝraŭbon is the direct object, and Esperanto marks direct objects with -n.

• ŝraŭbo = a screw / the screw
• ŝraŭbon = the screw (as the thing being acted on)

In this sentence, the screw is the thing being tightened, so it gets -n.

Compare:

• La ŝraŭbo falis. = The screw fell.
  
  • here ŝraŭbo is the subject
• Mi vidas la ŝraŭbon. = I see the screw.
  
  • here ŝraŭbon is the object

Because it comes after the preposition per.

In Esperanto, a noun after a preposition normally does not take the accusative -n just because it follows that preposition.

So:

• per la ŝraŭbturnilo = with the screwdriver / by means of the screwdriver

The screwdriver is not the direct object here. It is the tool used to perform the action.

Per means by means of, with, or using.

It introduces the instrument or method used to do something.

So:

• per la ŝraŭbturnilo = using the screwdriver

This is different from kun, which often means with in the sense of together with or accompanied by.

Compare:

• Mi skribas per krajono. = I write with a pencil.
  
  • pencil = instrument
• Mi iras kun mia amiko. = I am going with my friend.
  
  • friend = companion

So in your sentence, per is the natural choice because a screwdriver is a tool.

Because Esperanto uses la for each noun that is definite.

Here both nouns are treated as specific:

• la ŝraŭbon = the specific screw
• la ŝraŭbturnilo = the specific screwdriver

Esperanto has no indefinite article like English a/an. So the contrast is:

• ŝraŭbo = a screw / screw
• la ŝraŭbo = the screw

Using la twice is completely normal when both things are definite.

It is a very typical Esperanto compound word.

You can break it down like this:

• ŝraŭb- = screw
• turn- = turn
• -il- = tool or instrument for doing something
• -o = noun ending

So ŝraŭbturnilo literally means something like:

screw-turning tool

That is exactly how Esperanto often builds words: a root + another root + a suffix.

Other examples with -il-:

• tranĉilo = knife
  
  • tranĉi = to cut
• skribilo = writing instrument
• malfermilo = opener

Yes, it can be.

The basic idea of streĉi is to make tight, tense, or taut. Depending on context, that can be translated as:

• tighten
• strain
• stretch taut

With a screw, the intended meaning is clearly tighten.

Learners sometimes notice that in English stretch and tighten are not always the same thing, but Esperanto roots often cover a slightly different range of meanings than a single English word does. In context, streĉu la ŝraŭbon is understood naturally as tighten the screw.

A few letters here are especially worth noticing:

• ŝ = like English sh
• ĉ = like English ch
• ŭ is a short w-like sound, usually in diphthongs like aŭ

So:

• ŝraŭbo sounds roughly like SHROW-bo
• ŝraŭbturnilo starts with the same ŝraŭb-

Also remember that Esperanto stress is almost always on the second-to-last syllable:

• stre-ĈU
• ŝraŭ-BON
• ŝraŭb-tur-NI-lo

A rough pronunciation of the whole sentence is:

STREH-choo la SHROW-bon pehr la SHROWB-toor-NEE-lo

Yes, to some extent.

Esperanto word order is fairly flexible because the accusative -n helps show what the direct object is.

So the standard order:

• Streĉu la ŝraŭbon per la ŝraŭbturnilo.

could also be rearranged, for example:

• Per la ŝraŭbturnilo streĉu la ŝraŭbon.

That can put more emphasis on the tool.

However, the most neutral and natural version for a simple instruction is usually the original one: verb + object + per-phrase.

Usually, per is better here.

• per la ŝraŭbturnilo = using the screwdriver as a tool
• kun la ŝraŭbturnilo = with the screwdriver, but this can sound more like accompaniment or possession

In real usage, some people might still understand kun here, but per is the clearer and more standard choice when you mean by means of a tool.

A common way is to add bonvolu:

• Bonvolu streĉi la ŝraŭbon per la ŝraŭbturnilo.
  = Please tighten the screw with the screwdriver.

Notice that after bonvolu, Esperanto often uses the infinitive:

• Bonvolu atendi. = Please wait.
• Bonvolu sidiĝi. = Please sit down.

You can also simply add a polite word like mi petas in some contexts, but bonvolu is very common for polite instructions.

Because Esperanto has only one article: la, which means the.

There is no separate word for a/an.

So:

• ŝraŭbturnilo = screwdriver / a screwdriver
• la ŝraŭbturnilo = the screwdriver

You understand whether it is indefinite or just general from context when la is absent. This is very normal in Esperanto and something English speakers need a little time to get used to.