Der Temperaturfühler misst die Temperatur.

Because the two nouns have different grammatical genders:

• der Temperaturfühler = masculine
• die Temperatur = feminine

In German, every noun has a grammatical gender, and the article must match it.

A useful detail here: Temperaturfühler is a compound noun:

• Temperatur = temperature
• Fühler = probe / sensor / feeler

The final part of a compound usually determines the gender, and der Fühler is masculine, so the whole word is der Temperaturfühler.

Because in German, articles show not only gender but also case.

In this sentence:

• Der Temperaturfühler is the subject → nominative case
• die Temperatur is the direct object → accusative case

So the sentence breaks down like this:

• der = masculine nominative
• die = feminine accusative

For feminine nouns, die is the same in nominative and accusative, so die Temperatur does not change here.

The subject is the thing doing the action, and the object is the thing receiving the action.

Here:

• Der Temperaturfühler = the thing that measures
• misst = measures
• die Temperatur = the thing being measured

So:

• subject: der Temperaturfühler
• verb: misst
• object: die Temperatur

This is very similar to English word order in a basic statement: subject + verb + object.

Because messen is the infinitive, meaning to measure.

In the sentence, the subject is der Temperaturfühler, which is third person singular (it measures), so the verb has to be conjugated:

• ich messe = I measure
• du misst = you measure
• er/sie/es misst = he/she/it measures
• wir messen = we measure
• ihr messt = you all measure
• sie/Sie messen = they / you (formal) measure

So misst is the correct form for he/she/it.

Because messen is a strong verb with a vowel change in the present tense for du and er/sie/es:

• du misst
• er/sie/es misst

The stem vowel changes from e to i.

So although the infinitive is messen, the third-person singular form is misst.

Yes. German very often combines nouns into one compound word.

So instead of writing something like temperature sensor as two separate words, German commonly makes one noun:

• Temperatur
  • Fühler = Temperaturfühler

This is completely normal in German. The last part usually carries the core meaning, so a Temperaturfühler is a kind of Fühler.

Yes. In German, all nouns are capitalized.

So in this sentence:

• Temperaturfühler is capitalized
• Temperatur is capitalized

The verb misst is not capitalized because it is not a noun.

Yes, that is grammatically possible, but it changes the emphasis.

• Der Temperaturfühler misst die Temperatur.
  Neutral, standard word order.

• Die Temperatur misst der Temperaturfühler.
  This puts more focus on die Temperatur.

German allows more flexibility than English because case marking helps show what is subject and object. Still, the first version is the most natural as a simple statement.

Because many German nouns do not change form in the singular when used as a direct object.

Here:

• die Temperatur in nominative
• die Temperatur in accusative

The article shows the case, and the noun itself stays the same.

That is especially common with feminine singular nouns.

misst is pronounced roughly like mist in English, but with a short German i sound.

A simple approximation:

• misst ≈ mist

The ss is a sharp s sound.

So the whole sentence is approximately:

• Der Temperaturfühler misst die Temperatur.

A rough English-friendly pronunciation might be:

• dair tem-pe-ra-TOOR-fyoo-ler misst dee tem-pe-ra-TOOR

That is only an approximation, but it can help at first.

Other words are possible depending on context.

For example, German might also use:

• Temperatursensor = temperature sensor
• Temperatursonde = temperature probe

But Temperaturfühler is a perfectly normal and understandable word. It suggests a device or probe that senses temperature.

So this sentence is grammatically straightforward and natural.