Ju pli klare vi skribas la adreson kaj la numeron, des pli rapide mi ricevas la pakon.

It is the standard Esperanto pattern for the more ... the more ..., the more ... the less ..., and similar comparisons.

In this sentence:

Ju pli klare vi skribas la adreson kaj la numeron, des pli rapide mi ricevas la pakon.

the structure means:

The more clearly you write the address and the number, the more quickly I receive the package.

A good way to remember it is:

• ju = introduces the changing condition
• des = introduces the result that changes along with it

So:

• Ju pli ... , des pli ... = The more ... , the more ...
• Ju malpli ... , des malpli ... = The less ... , the less ...

Because the sentence compares two increasing things:

• how clearly you write
• how quickly I receive

So:

• ju pli klare = the more clearly
• des pli rapide = the more quickly

Here pli means more, and it modifies the adverbs klare and rapide.

This is very natural in Esperanto. You often see:

• pli granda = bigger / more big
• pli rapide = more quickly / faster
• pli klare = more clearly

Because they are adverbs.

In Esperanto:

• -a = adjective, describes a noun
• -e = adverb, describes a verb, adjective, or another adverb

Here they describe how the actions happen:

• skribas — how do you write? klare = clearly
• ricevas — how do I receive? rapide = quickly

Compare:

• klara adreso = a clear address

• vi skribas klare = you write clearly

• rapida livero = a fast delivery
• la pako alvenas rapide = the package arrives quickly

They are direct objects, so they take the accusative ending -n.

In Esperanto, the direct object is the thing directly affected by the verb.

Here:

• vi skribas la adreson kaj la numeron
  You write the address and the number
• mi ricevas la pakon
  I receive the package

So:

• adreso → adreson
• numero → numeron
• pako → pakon

That -n is very important in Esperanto grammar.

Both are possible depending on context, but la is used here because the speaker means a specific address and a specific number—probably the address and number that belong on the package.

Using la often sounds like:

• the address
• the number

rather than just any address or any number.

Esperanto often uses la in places where English also uses the, but learners should know that Esperanto la is very regular: it never changes for gender, number, or case, except that the noun after it may take -n if needed.

In context, it most likely means a number connected with the address, such as:

• the house number
• an apartment number
• some other delivery number

Esperanto numero simply means number, so the exact meaning comes from context.

If the speaker wanted to be more specific, they might say:

• la stratnumeron = the street number / house number
• la apartamentan numeron = the apartment number

But in many real sentences, just la numeron is enough because the situation makes it clear.

Yes, Esperanto word order is fairly flexible, but this order is the most natural and clear.

The basic pattern is:

Ju + comparative expression + clause, des + comparative expression + clause

So the sentence is built like this:

• Ju pli klare = the more clearly
• vi skribas la adreson kaj la numeron = you write the address and the number
• des pli rapide = the more quickly
• mi ricevas la pakon = I receive the package

You could rearrange parts for emphasis, but learners should usually stick to this standard pattern.

No, they are different.

• pli rapide = more quickly / faster
  This is a comparison
• rapidege = very quickly / extremely quickly
  This is an intensification

So:

• Ju pli rapide, des pli bone. = The faster, the better.
• Li kuris rapidege. = He ran very fast.

In your sentence, the speaker is comparing one degree with another, so pli rapide is the correct choice.

Both are possible, but they mean slightly different things.

• mi ricevas la pakon = I receive the package
• la pako alvenas = the package arrives

The original sentence focuses on the receiver's experience: if you write more clearly, I receive it more quickly.

If the sentence said la pako alvenas pli rapide, the focus would be more on the package's arrival itself.

So this is a choice of meaning, not just grammar.

It can be used with other comparative ideas too, not only pli.

For example:

• Ju malpli vi dormas, des pli laca vi estas.
  The less you sleep, the more tired you are.

• Ju pli frue ni ekiras, des pli bone.
  The earlier we leave, the better.

• Ju pli longa estas la vojo, des malpli mi volas iri.
  The longer the road is, the less I want to go.

So the important thing is the correlative comparison, not just the word pli.

Yes—three very useful Esperanto habits appear here:

1. Use the regular comparison pattern

   • ju ... des ... = the more ... the more ...

2. Watch adverb endings

   • klare, rapide end in -e because they describe verbs

3. Do not forget the accusative -n

   • adreson
   • numeron
   • pakon

If you understand those three things, you understand most of the grammar of this sentence.