Odečet je správný.

Because správný has to agree with odečet.

• odečet is a masculine singular noun
• so the adjective also appears in the masculine singular nominative form: správný

A few comparison examples:

• výpověď je správná = the statement is correct
• číslo je správné = the number is correct
• odečet je správný = the reading/subtraction is correct

So the ending -ý is there because of grammatical agreement.

It is in the nominative case, because it is the subject of the sentence.

In Odečet je správný:

• odečet = the subject
• je = the verb is
• správný = a predicate adjective describing the subject

Since správný describes the subject, it is also in the nominative.

Je is the 3rd person singular present tense of být = to be.

So:

• je = is

This is the normal Czech way to link a noun with an adjective:

• Dům je velký. = The house is big.
• Film je zajímavý. = The film is interesting.
• Odečet je správný. = The reading/subtraction is correct.

Unlike in some headline-style language, in a normal full sentence Czech usually keeps je here.

Because after být = to be, Czech normally uses an adjective, not an adverb, when describing a noun.

Here, správný describes odečet, so it must be an adjective.

Compare:

• Odečet je správný. = The reading/subtraction is correct.
  
  • správný describes the noun odečet

But:

• Počítáš správně. = You are calculating correctly.
  
  • správně describes the verb počítáš

So:

• správný = correct, right, accurate for a noun
• správně = correctly for an action

Odečet is a noun. It can mean different things depending on context, most commonly:

• a subtraction in mathematics
• a reading or readout from a meter, gauge, or instrument

It comes from the verb odečíst / odečítat, which can mean things like:

• to subtract
• to read off a value from a device

So a learner may see odečet in both school math and technical contexts.

Yes. It is related to the verb odečíst or its imperfective partner odečítat.

Very roughly:

• odečíst = to subtract / to read off
• odečítat = to be subtracting / to read off repeatedly
• odečet = subtraction / reading / readout

This is very common in Czech: a noun is formed from a verb and names the action or its result.

Because Czech does not have articles like English a and the.

So Odečet je správný can mean:

• The reading is correct
• The subtraction is correct
• sometimes even A reading is correct, depending on context

Czech usually shows definiteness through context rather than a separate article.

Yes, Czech word order is flexible, but the neutral, ordinary order here is:

• Odečet je správný.

You may also see other orders for emphasis, for example:

• Správný je odečet.
• Správný odečet je... in a larger sentence

But those are less neutral and usually sound as if something is being contrasted or emphasized.

For a basic statement, Odečet je správný is the most natural choice.

A simple learner-friendly pronunciation is:

OH-deh-chet yeh SPRAAV-nee

A few points:

• Czech stress is usually on the first syllable of each word
• č sounds like ch in check
• j in je sounds like y in yes
• á is a long vowel
• ý is also long, and in modern Czech it sounds basically like a long ee

So:

• odečet ≈ OH-deh-chet
• je ≈ yeh
• správný ≈ SPRAAV-nee

In the plural, both the verb and the adjective change:

• Odečty jsou správné. = The readings/subtractions are correct.

Changes:

• odečet → odečty
• je → jsou
• správný → správné

This is another example of agreement: the adjective and verb match the noun.