onaka ga itai node, kyou ha ie de yasumimasu.

ので connects the reason to the result, so it means something like because or so.

• お腹が痛いので = because my stomach hurts
• 今日は家で休みます = I will rest at home today

Compared with から, ので usually sounds a bit softer, calmer, and more explanatory.

• お腹が痛いから、今日は家で休みます。
• お腹が痛いので、今日は家で休みます。

Both are natural, but ので often feels slightly more polite or less direct.

Because 痛い is an i-adjective, not a verb.

In Japanese, the thing that hurts is usually marked with が:

• 頭が痛い = my head hurts
• 喉が痛い = my throat hurts
• お腹が痛い = my stomach hurts

Using を would not be natural with 痛い in this pattern.

So:

• お腹が痛い = correct
• お腹を痛い = incorrect

痛い is an i-adjective.

Even though English uses a verb in my stomach hurts, Japanese says something closer to my stomach is painful.

That is why the structure is:

• お腹 = stomach / belly
• が = marks what is painful
• 痛い = painful

This is a very common pattern in Japanese with body parts and sensations.

Japanese often leaves out subjects when they are clear from context.

In this sentence, it is obvious that the speaker is talking about themself:

• My stomach hurts
• Today I will rest at home

So Japanese does not need 私は or 僕は or 私は unless the speaker wants extra emphasis or clarity.

A full version could be:

• 私は、お腹が痛いので、今日は家で休みます。

But in normal conversation, leaving out I is more natural.

Both can appear, but 今日は marks today as the topic or time frame.

So 今日は gives a sense like:

• as for today
• today, at least
• today, specifically

Compare:

• 今日は家で休みます = As for today, I will rest at home
• 今日家で休みます = also understandable, but slightly less marked

Using は after time words is very common when the speaker wants to set the scene or contrast that time with others.

Because で marks the place where an action happens.

Here, the action is 休みます:

• 家で休みます = rest at home

Use で for the location of an action:

• 学校で勉強します = study at school
• 部屋で寝ます = sleep in the room
• 家で休みます = rest at home

に is often used for destination or existence, not the location of this kind of action.

Here, 休みます means rest.

So 家で休みます means the speaker will stay home and rest because of the stomachache.

Depending on context, 休む can mean different things:

• 少し休みます = I will rest for a bit
• 学校を休みます = I will be absent from school
• 仕事を休みます = I will take the day off work

In this sentence, because it says 家で, the meaning is clearly rest at home.

The お in お腹 is an honorific or polite prefix. It often appears with certain common words, including some body-related words.

So:

• 腹 = belly / stomach
• お腹 = the more common polite everyday form

In modern everyday Japanese, お腹 is much more natural than 腹 in ordinary conversation, especially in polite speech.

A learner should usually memorize お腹 as the normal word.

The comma helps separate the reason part from the main statement.

• お腹が痛いので、 = because my stomach hurts,
• 今日は家で休みます。 = I will rest at home today.

Japanese commas are often used more flexibly than English commas. In a sentence like this, the comma is very common because it makes the sentence easier to read.

You may also see similar sentences without a comma in casual writing, but with ので it is very natural to include one.

The basic meaning stays the same, but Japanese word order can be somewhat flexible, especially with time expressions.

This sentence is very natural:

• お腹が痛いので、今日は家で休みます。

You could also say:

• 今日は、お腹が痛いので、家で休みます。

Both work, but the focus changes slightly.

• Putting お腹が痛いので first emphasizes the reason first.
• Putting 今日は earlier sets the time frame first.

The verb 休みます still comes at the end, which is the most important fixed part.

No. Normal Japanese writing usually does not use spaces between words.

The spaces here are only for learners, to make the sentence easier to read:

• お腹 が 痛い ので、今日 は 家 で 休みます。

In ordinary Japanese, it would normally be written as:

• お腹が痛いので、今日は家で休みます。

So the spaces are a teaching aid, not standard writing.