Plyn je spíš levný.

Spíš usually means rather, quite, more on the ... side, or fairly in this kind of sentence.

So Plyn je spíš levný suggests something like:

• Gas is rather cheap
• Gas is fairly cheap
• Gas is more on the cheap side

It often makes the statement sound a bit softer or less absolute than simply saying Plyn je levný.

Because levný is an adjective, and here it is describing plyn after the verb je.

In Czech, after být (to be), you normally use an adjective that agrees with the noun:

• Plyn je levný. = Gas is cheap.
• Voda je studená. = The water is cold.

By contrast, levně is an adverb, meaning cheaply:

• Prodává to levně. = He/she sells it cheaply.

So:

• levný = cheap
• levně = cheaply

The adjective has to agree with plyn in gender, number, and case.

Here, plyn is:

• masculine inanimate
• singular
• nominative

So the adjective also takes the matching form:

• levný

Compare:

• plyn → levný
• voda → levná
• auto → levné

So the ending -ý tells you that the adjective matches a masculine singular noun like plyn.

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

The basic structure is:

• Plyn = subject
• je = is
• spíš levný = predicate description

So this is a standard nominative subject + být + adjective pattern.

Because Czech does not use articles like English does.

So plyn can mean:

• gas
• the gas
• sometimes even a gas, depending on context

You figure out the exact meaning from the situation, not from an article.

That is very normal in Czech.

Not always exactly.

Plyn means gas in the sense of a gaseous substance or fuel, especially things like:

• natural gas
• household gas
• gas as a physical substance

It does not normally mean gasoline/petrol.
So if an English speaker thinks of gas as fuel for a car, Czech usually does not use plyn for that meaning.

Also, in some contexts jet na plyn can refer to running on gas fuel, but plyn itself is not the ordinary word for gasoline.

Je is the 3rd person singular present form of být (to be).

So:

• já jsem = I am
• ty jsi = you are
• on/ona/ono je = he/she/it is

Since plyn is singular, Czech uses je:

• Plyn je levný. = Gas is cheap.

Unlike some languages, Czech normally keeps the verb to be in this kind of present-tense sentence.

Yes, Czech word order is flexible, but the given order is the most neutral and natural:

• Plyn je spíš levný.

This presents the sentence in a straightforward way: subject first, then verb, then the description.

You may see other orders in special contexts for emphasis, but they can sound marked or less neutral. For a learner, the safest default is:

• subject + je + spíš + adjective

So this sentence is a very good standard pattern to copy.

No.

• spíš levný = rather cheap / fairly cheap
• levnější = cheaper

So spíš levný does not necessarily compare gas with something else directly. It just places it on the cheaper side.

By contrast, levnější is a true comparative:

• Plyn je levnější než elektřina. = Gas is cheaper than electricity.

So spíš is about nuance, while -ější / comparative forms are about comparison.

Roughly like speesh.

A few details:

• s = like English s
• p = like English p
• í = a long ee sound
• š = like English sh

So:

• spíš ≈ speesh

The long vowel í is important: it is held a bit longer than a short i would be.

Roughly: LEV-nee

A few notes:

• le- sounds like leh
• vný can be tricky for English speakers
• the ý is a long vowel, somewhat like a long ee sound, though not identical to English ee

A practical learner pronunciation is:

• levný ≈ LEV-nee

The stress in Czech is normally on the first syllable, so:

• LEV-ný

Yes.

• Plyn je levný. = Gas is cheap.
• Plyn je spíš levný. = Gas is rather/fairly cheap.

Without spíš, the statement is stronger and more direct.
With spíš, it sounds a bit more cautious, nuanced, or approximate.

So both are correct; they just do not sound exactly the same.