daikon wo tiisaku kitte kara, kinoko to udon no suupu ni iremasu.

を marks the direct object of the verb. Here, 大根 is the thing being handled: it is what gets cut.

In this sentence, 大根 is also understood to be the thing that later gets added to the soup, even though Japanese does not repeat it.

小さく is the adverbial form of the い-adjective 小さい.

• 小さい = small
• 小さく = smallly / into a small form / in a small way

With verbs like 切る, this adverbial form describes the result or manner of the action:

• 大根を小さく切る = cut the daikon small / cut the daikon into small pieces

If you said 小さい大根, that would mean a small daikon, not cut it small.

切ってから means after cutting or cut it, and then...

It is made from:

• 切る = to cut
• 切って = te-form
• から = after

So Vてから is a very common pattern meaning:

after doing V, do the next thing

Here it shows the order of steps clearly: first cut the daikon, then add it.

No. In this sentence, から means after, not because.

That is because it comes after a te-form verb:

• 切ってから = after cutting

Compare:

• 時間がないから、急ぎます。 = Because I have no time, I hurry.
• 食べてから、出かけます。 = After eating, I go out.

So から can mean different things depending on the pattern.

Yes, it could.

• 切って、入れます。
• 切ってから、入れます。

Both can mean that one action happens before the next. But てから makes the sequence more explicit: do X first, and only after that do Y.

In recipes and instructions, Vてから is very common because it makes the steps clear.

Yes. The thing being added is still 大根, but Japanese leaves it unstated in the second part because it is already obvious.

A fuller version would be:

大根を小さく切ってから、（大根を）きのことうどんのスープに入れます。

Japanese often omits repeated words when the meaning is clear from context.

Here, と means and. It connects two nouns:

• きのこ = mushrooms
• うどん = udon

So きのことうどん means mushrooms and udon.

This is the noun-linking と, not the quotation と and not the with meaning.

The phrase means something like mushroom-and-udon soup or soup with mushrooms and udon.

The structure is:

• きのことうどん = mushrooms and udon
• 〜のスープ = soup of / soup with / soup related to 〜

So the の connects the whole noun phrase to スープ.

Even though の comes after うどん, the meaning is not just udon soup with separate mushrooms floating around grammatically. In context, きのこ and うどん are grouped together before スープ.

に marks the destination or container that something goes into.

With 入れる:

• thing being put in = object
• place/container = marked by に

So:

• スープに入れる = put it into the soup

This is different from:

• スープを入れる = add/pour the soup itself

So に is used because the soup is the place the daikon goes into.

入れます is the polite non-past form of 入れる.

• dictionary form: 入れる
• polite form: 入れます

In recipes, Japanese often uses this polite non-past form to describe steps. In English, we often translate that kind of sentence more like an instruction:

• add it
• then add it

So it is not necessarily plain present tense in the English sense.

Because Japanese often omits the subject when it is obvious.

In a recipe, the understood subject is basically you or the cook. Japanese does not need to say あなたは here.

This is very normal. Recipe and instruction language often leaves out:

• the subject
• repeated objects
• other information that is already clear from context

Normally, Japanese is written without spaces.

So the natural written sentence is:

大根を小さく切ってから、きのことうどんのスープに入れます。

Spaces are often added in learning materials to help beginners see the parts more easily. They are not usually used in normal Japanese writing.