Služba byla tehdy levná.

Because byla is the past-tense form of být (to be) used with a feminine singular subject.

Here, the subject is služba, and služba is a feminine noun, so the verb must match it:

• byl = masculine singular
• byla = feminine singular
• bylo = neuter singular
• byli / byly = plural

So:

• Služba byla... = correct, because služba is feminine.

Because levná is an adjective, and it agrees with služba in gender, number, and case.

Since služba is:

• feminine
• singular
• nominative

the adjective must also be feminine singular nominative:

• masculine: levný
• feminine: levná
• neuter: levné

So:

• levná služba = cheap service
• Služba byla levná = The service was cheap

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

In Služba byla tehdy levná, the thing being talked about is služba, so it is the subject and stays in the nominative.

Also, after být in this kind of sentence, Czech normally uses a predicate adjective that matches the subject, so levná is also in nominative form.

Tehdy means then, at that time, or back then, depending on context.

In this sentence, it most naturally means something like:

• The service was cheap then
• The service was cheap at that time
• The service was cheap back then

So tehdy is an adverb of time.

Yes. Czech word order is much more flexible than English word order.

This sentence can appear in different orders, for example:

• Služba byla tehdy levná.
• Tehdy byla služba levná.
• Služba tehdy byla levná.

All of these are grammatical, but the emphasis changes slightly.

Very roughly:

• Služba byla tehdy levná. = neutral
• Tehdy byla služba levná. = emphasizes back then
• Služba tehdy byla levná. = also possible, often with a slightly different rhythm or focus

Czech often uses word order to show what is already known and what is new or emphasized.

Because Czech does not have articles like English a / an / the.

So služba can mean:

• service
• a service
• the service

The exact meaning depends on context.

That is why Služba byla tehdy levná can be translated as The service was cheap then even though there is no separate word for the in Czech.

Not always. Služba can mean several related things, depending on context, such as:

• service (a commercial or public service)
• duty
• shift
• military service

In this sentence, if the meaning shown to the learner is service, that is the sense you should use. But it is good to know that the noun is broader than the English word service in some contexts.

A few useful points:

• Czech stress is usually on the first syllable of each word.
• ž is pronounced like the s in measure.
• á is a long vowel.

A rough pronunciation guide:

• Služba ≈ SLOOZH-ba
• byla ≈ BIH-la
• tehdy ≈ TEH-hdi
• levná ≈ LEV-naa

A more careful note:

• In normal speech, tehdy is often pronounced approximately TEG-di or TEH-di, depending on speaker and style.

It is in the past tense.

The past tense is shown by byla, the past form of být (to be).

So the structure is:

• služba = subject
• byla = was
• tehdy = then / back then
• levná = cheap

So the whole sentence is describing a past situation.

Yes, it is possible, but it is less neutral than Služba byla tehdy levná.

Putting tehdy at the end gives it stronger focus, almost like:

• The service was cheap then
• It was then that the service was cheap

So it is grammatical, but the original version sounds more natural as a plain statement.

Yes. Levný / levná / levné is the normal, neutral Czech adjective for cheap or inexpensive.

You may also encounter laciný, which can sometimes mean cheap, but it often has a more negative sense, like:

• low-quality
• tacky
• cheap in a bad way

So in most ordinary situations, levný is the safer and more natural word.