Egzamin był trudny, ale mój wynik jest dobry.

Polish does not have articles like English the and a/an.

So:

• Egzamin can mean the exam or an exam
• wynik can mean the result or a result

You understand which one is meant from context. In this sentence, Egzamin is naturally understood as the exam, and mój wynik as my result.

Both are in the nominative case because they are the subjects of their clauses:

• Egzamin był trudny = The exam was difficult
• mój wynik jest dobry = my result is good

In Polish, the noun after być can stay in the nominative when you are describing what something is like with an adjective, as in:

• egzamin był trudny
• wynik jest dobry

Był is the past tense of być = to be.

So:

• jest = is
• był = was for a masculine singular subject

Since the exam happened in the past, Polish uses był:

• Egzamin był trudny = The exam was difficult

The form był agrees with egzamin, which is masculine singular.

Because the speaker is talking about the result as something true now.

• Egzamin był trudny = the exam took place in the past
• mój wynik jest dobry = my result is good now

This tense combination is perfectly natural. English does the same:

• The exam was hard, but my result is good

If you said mój wynik był dobry, that would mean my result was good, which sounds as if you are talking about the past state of the result rather than its current status.

Because mój must agree with the noun it describes.

Wynik is:

• masculine
• singular
• nominative

So the possessive adjective must also be masculine singular nominative:

• mój wynik = my result

Compare:

• mój egzamin = my exam
• moja książka = my book
• moje zadanie = my task

So moje wynik is incorrect because moje does not match the gender and form of wynik.

Because they are describing masculine singular nominative nouns:

• egzamin → trudny
• wynik → dobry

In Polish, adjectives must agree with the noun in:

• gender
• number
• case

So here the pattern is:

• masculine singular nominative noun + masculine singular nominative adjective

That gives forms like:

• trudny egzamin
• dobry wynik

In Polish, a comma is normally used before coordinating conjunctions like ale when they connect clauses.

So:

• Egzamin był trudny, ale mój wynik jest dobry.

This is standard Polish punctuation.

Ale means but, and it introduces a contrast between the two ideas:

• the exam was difficult
• the result is good

Not completely. Polish word order is more flexible than English because endings carry a lot of grammatical information.

The sentence:

• Egzamin był trudny, ale mój wynik jest dobry.

is a very natural, neutral order.

You could also say:

• Mój wynik jest dobry, ale egzamin był trudny.

That changes the focus slightly by starting with the result.

You could even move words around for emphasis, but the original version is the most straightforward for a learner.

These two words can feel unusual for English speakers.

• mój sounds roughly like mooy or moy, with a vowel similar to the oy in boy, but a bit different depending on accent
• był is harder:
  • b = normal b
  • y is a Polish vowel with no exact English equivalent; it is not the same as English ee
  • ł is pronounced like English w

So był sounds roughly like biw or bew with a special Polish vowel in the middle.

Also note:

• ó is pronounced like u
• ł is pronounced like w

Polish usually stresses the second-to-last syllable of a word.

So:

• egZAmin
• trudny → TRUDny
• wynik → WYnik
• dobry → DObry

Monosyllabic words like mój, był, and jest just carry stress naturally when spoken.

Sometimes, but trudny is the more natural word here.

• trudny = difficult, hard
• ciężki literally means heavy, and can also mean hard/tough in some contexts

For an exam, trudny egzamin is the standard choice if you mean the questions were difficult.

So:

• Egzamin był trudny = the normal, natural way to say The exam was difficult

Polish often expresses contrast exactly the same way English does: with two clauses linked by ale.

So the structure is:

• Egzamin był trudny
• ale
• mój wynik jest dobry

This is a very natural and clear way to show:

• one thing was negative
• another thing was positive

It is simple, idiomatic Polish.