Scrivo una riga nel quaderno.

In Italian, the subject pronoun is often omitted because the verb ending already shows who is doing the action.

• scrivo = I write / I am writing
• The ending -o tells you it is first person singular: I

So Scrivo una riga nel quaderno is naturally understood as I write a line in the notebook.

You could say Io scrivo una riga nel quaderno, but io would usually add emphasis, as in I am writing a line.

Scrivo is the present indicative of the verb scrivere.

Here it can mean either:

• I write
• I am writing

Italian often uses the simple present where English might use either the simple present or the present continuous, depending on context.

The base form, or infinitive, is scrivere, meaning to write.

A few present-tense forms are:

• io scrivo = I write
• tu scrivi = you write
• lui/lei scrive = he/she writes
• noi scriviamo = we write
• voi scrivete = you all write
• loro scrivono = they write

So scrivo is the io form of scrivere.

Because riga is a feminine singular noun.

In Italian:

• un is usually used with masculine singular nouns
• una is used with feminine singular nouns

So:

• una riga = a line
• un quaderno = a notebook

The article has to match the gender of the noun.

Here riga means line, as in a line of writing.

Depending on context, riga can also mean:

• a line on paper
• a row
• a stripe

In Scrivo una riga nel quaderno, the most natural meaning is a line of writing in the notebook.

Nel is the contracted form of in + il.

So:

• in + il = nel

This is very common in Italian. Prepositions often combine with definite articles:

• nel = in the
• sul = on the
• dal = from the
• al = to the

So nel quaderno literally means in the notebook.

Quaderno is a masculine singular noun, so its definite article is il.

That gives:

• il quaderno = the notebook

After the preposition in, it becomes:

• nel quaderno = in the notebook

Italian articles depend on gender, number, and sometimes the first sound of the following word. Since quaderno is masculine singular and begins with a normal consonant sound, il is the correct article.

Italian commonly uses in with things like notebooks, books, journals, and similar objects when talking about writing inside them.

So:

• nel quaderno = in the notebook

English sometimes uses in too, but learners may expect on because you write on paper. In Italian, in a notebook is the natural expression when you mean writing as part of its contents.

If you said sul quaderno, that would sound more like on the notebook, meaning on its surface, such as on the cover.

Yes. Because it uses the definite article il, it means in the notebook, not just in a notebook.

• nel quaderno = in the notebook
• in un quaderno = in a notebook

So the sentence refers to a specific notebook, either already known from context or understood by the speaker and listener.

The normal, neutral word order here is:

• Scrivo = I write
• una riga = a line
• nel quaderno = in the notebook

So the full sentence is very standard and natural.

Italian word order is more flexible than English, but changing it usually changes the emphasis. For example:

• Scrivo una riga nel quaderno = neutral
• Nel quaderno scrivo una riga = emphasizes where I write
• Una riga scrivo nel quaderno = emphasizes a line

For a beginner, the original order is the best one to learn first.

Yes. Sto scrivendo una riga nel quaderno means I am writing a line in the notebook and makes the ongoing action more explicit.

Compare:

• Scrivo una riga nel quaderno = I write / I am writing a line in the notebook
• Sto scrivendo una riga nel quaderno = I am writing a line in the notebook

In many everyday situations, Italian simply uses the present tense scrivo, where English might prefer I am writing. Both are possible, but the simple present is very common in Italian.