hyousi ga aoi nooto no zyuupeezi ni, zikosyoukai wo kakimasita.

A helpful way to chunk it is:

• 表紙が青い = whose cover is blue
• 表紙が青いノート = the notebook whose cover is blue
• 表紙が青いノートの十ページに = on page 10 of the notebook whose cover is blue
• 自己紹介を書きました = (I) wrote a self-introduction

So the whole sentence is built like this:

• [description of the notebook] + [which page] + [where particle に] + [what was written] + [verb]

Japanese often puts all the descriptive information before the noun it describes.

Because in Japanese, clauses that describe a noun go before that noun.

So:

• 表紙が青いノート literally = cover is blue notebook
• natural English = a notebook whose cover is blue / a notebook with a blue cover

This is called a relative clause in English grammar terms. Japanese does not need words like that, which, or whose here. It simply places the descriptive clause directly before the noun.

Here, 表紙 is the thing that is blue, so が marks it as the subject of 青い.

• 表紙が青い = the cover is blue

Even though the whole clause modifies ノート, inside that clause 表紙 still has its own grammatical role, and が marks that role.

This is very common in Japanese:

• 髪が長い人 = a person whose hair is long
• 目が大きい猫 = a cat whose eyes are big
• 表紙が青いノート = a notebook whose cover is blue

Usually, 表紙が青いノート is the natural choice.

Using は inside a noun-modifying clause is much less common here because は adds a topic/contrast feeling, while が simply marks cover as the thing that has the property blue.

So:

• 表紙が青いノート = neutral, natural
• 表紙は青いノート = sounds contrastive, like as for the cover, it is blue..., which is usually not what you want here

In short: for a straightforward description, が is the expected particle.

Sometimes, yes. You may also hear:

• 表紙の青いノート

This can also mean a notebook with a blue cover.

However, for many learners, 表紙が青いノート is the safest and most standard pattern to learn first. In modifier clauses, が is very common and clear. の can sometimes appear in similar patterns, especially with body parts or inherent attributes, but が and の are not always freely interchangeable in every sentence.

So for this sentence, が is completely natural and probably the form you should be most comfortable with first.

It means page 10 of the notebook.

Here, の links the two nouns:

• ノート = notebook
• 十ページ = page 10 / the tenth page, depending on context

So:

• ノートの十ページ = the notebook’s page 10 = page 10 of the notebook

This is a very common use of の to show relationship, possession, or belonging.

Because に marks the place where the writing ends up.

With 書く, に is often used for the surface/location where something is written:

• ノートに書く = write in a notebook
• 紙に書く = write on paper
• ページに書く = write on a page

So:

• 十ページに = on page 10

Even though English says on page 10, Japanese uses に here.

It can mean either, depending on context.

In this sentence, it means page 10, because it is followed by に and refers to a location where something was written:

• ノートの十ページに = on page 10 of the notebook

If it meant a quantity, it would be something like:

• 十ページ書きました = I wrote ten pages

So context tells you which meaning is intended.

Also:

• 十ページ目 = the tenth page (more explicitly ordinal)
• 第十ページ = page 10 in a more formal or book-like style

But 十ページに is perfectly natural here.

Because 自己紹介 is the direct object of 書きました.

• 自己紹介を = a self-introduction
• 書きました = wrote

So を marks what was written.

This works the same way as:

• 名前を書く = write a name
• 手紙を書く = write a letter
• 作文を書く = write a composition
• 自己紹介を書く = write a self-introduction

Because the sentence is describing a completed action:

• 書きました = wrote
• non-past would be 書きます = write / will write

In Japanese, past tense often means the action is finished. So this sentence says the self-introduction has already been written.

Also, 書きました is the polite form. The plain form would be:

• 書いた

The subject is omitted, which is extremely common in Japanese.

From context, the understood subject is usually:

• I wrote
• or sometimes someone wrote, if the context makes that clear

So 自己紹介を書きました naturally means I wrote a self-introduction unless the surrounding context suggests someone else.

Japanese often leaves out subjects and topics when they are already understood.

Because 自己紹介 already means self-introduction, and Japanese often leaves possession implied when it is obvious.

In English, I wrote a self-introduction usually already implies my self-introduction. Japanese does the same kind of thing here.

If you really wanted to be extra explicit, context would usually handle it rather than adding a possessive word.

Some parts are flexible, but the structure of the modifiers must stay together.

This part needs to stay in front of ノート:

• 表紙が青いノート

And 十ページに needs to stay as the location phrase.

You could say:

• 表紙が青いノートの十ページに自己紹介を書きました。

The comma after に just adds a pause; it is not essential.

Japanese word order is often flexible with larger phrases, but the internal order of noun modifiers is much less flexible. You cannot split 表紙が青い away from ノート if you want it to describe the notebook.

Yes. 青い is an i-adjective, and here it directly describes 表紙 inside the clause:

• 表紙が青い = the cover is blue

Then that whole clause describes ノート.

So 青い is not directly modifying ノート by itself. It is part of the larger description 表紙が青い, which modifies ノート.

That is why the meaning is not a blue notebook in the simple sense, but more specifically a notebook whose cover is blue.