kaisetu wo yomimasita.

It is read:

かいせつ を よみました。
Romanization: kaisetsu o yomimashita.

A small pronunciation note: the particle を is written を but is pronounced お in modern Japanese.

解説 means something like explanation, commentary, or guide/explanatory notes.

The exact translation depends on context:

• in a book or article: explanation
• for a game, movie, or event: commentary
• for something technical: explanatory notes

So 解説を読みました could mean I read the explanation or I read the commentary, depending on the situation.

を marks the direct object of the verb—the thing that is being read.

So in this sentence:

• 解説 = the explanation/commentary
• を = marks it as the thing being read
• 読みました = read

So the structure is:

[thing read] + を + [read]

In other words, を is the particle that tells you what the action is being done to.

Japanese often leaves out the subject when it is obvious from context.

So instead of saying 私は解説を読みました, Japanese often just says:

解説を読みました。

The listener usually understands who did the action from the situation. In English, you usually need I, he, she, etc., but Japanese often omits them.

読みました is the polite past affirmative form of the verb 読む (to read).

Breakdown:

• dictionary form: 読む = to read
• polite non-past: 読みます = read / will read
• polite past: 読みました = read

So 読みました means read in a polite way.

読む is a godan verb.

To make the polite -ます form:

• 読む → change む to the i-stem み
• then add ます

So:

• 読む → 読みます
• past polite: 読みます → 読みました

This is a very common pattern for godan verbs.

Yes, 読みました is past.

Depending on context, English may translate it as:

• I read it
• I did read it
• I have read it

Japanese past tense does not match English tenses one-to-one. The important point is that the reading action is completed.

The plain version is:

解説を読んだ。

Here:

• polite: 読みました
• plain past: 読んだ

You would use 読んだ with friends, in casual speech, or in informal writing.

This is because 読む is a godan verb, and its plain past form is irregular in a predictable pattern.

For verbs ending in む, ぶ, or ぬ, the past form becomes んだ:

• 読む → 読んだ
• 遊ぶ → 遊んだ
• 死ぬ → 死んだ

So 読んだ is the correct plain past form.

It is common, but a little more formal or specific than a basic word like 説明.

A rough comparison:

• 説明 = explanation in a broad, everyday sense
• 解説 = explanation/commentary that often goes into detail or helps interpret something

For example, 解説 is very natural for:

• textbook notes
• article commentary
• expert analysis
• explanatory sections in media

Yes, but it changes the nuance.

• 説明を読みました = I read the explanation/instructions
• 解説を読みました = I read the commentary/explanatory notes/analysis

説明 is broader and often more practical.
解説 often sounds more like a detailed explanation or commentary.

Japanese normally puts the verb at the end. That is one of the most important basic sentence patterns in Japanese.

So:

解説を = the explanation
読みました = read

Japanese often follows a pattern like:

topic/subject + object + verb

Even when the subject is omitted, the verb usually still comes last.

In normal Japanese writing, you would usually write it without spaces:

解説を読みました。

Spaces are often added in learning materials to make the parts easier to see:

• 解説
• を
• 読みました

So the spaces are for learners, not standard Japanese spelling.

You would usually say:

解説を読んでいます。

This is the -ている form, which often expresses an ongoing action.

So:

• 解説を読みました = I read the explanation / I have read the explanation
• 解説を読んでいます = I am reading the explanation

In polite Japanese:

解説を読みましたか。

You just add か to make it a question.

Breakdown:

• 解説を読みました。 = I/you/he/she read the explanation.
• 解説を読みましたか。 = Did you read the explanation?

As usual, the subject is omitted unless needed.

In polite form, that would be:

解説を読みませんでした。

Breakdown:

• 読みました = read
• 読みませんでした = did not read

So this is the polite past negative form of 読む.