Przekazuję bluzkę z aksamitu tylko wtedy, gdy nie ma plamy.

Because bluzkę is the accusative singular form of bluzka.

In this sentence, bluzkę is the direct object of przekazuję (I hand over / pass on), so Polish changes the ending:

• bluzka = nominative singular
• bluzkę = accusative singular

This is a very common pattern for feminine nouns ending in -a:

• mam książkę = I have a book
• widzę kobietę = I see a woman
• przekazuję bluzkę = I hand over the blouse

Because here z means made of / from, and in that meaning it takes the genitive case.

So:

• aksamit = velvet
• z aksamitu = made of velvet

This is different from another use of z, where it means with and takes the instrumental:

• z kolegą = with a friend
• z aksamitu = of/from velvet

So the case depends on the meaning of z.

Yes. Both are possible.

• bluzka z aksamitu = a blouse made of velvet
• aksamitna bluzka = a velvet blouse

The version with z + genitive stresses the material a bit more explicitly. The adjective version is more compact. In many contexts, both sound natural.

Przekazuję comes from przekazywać / przekazać. It can mean:

• hand over
• pass on
• transfer
• deliver

It is often a bit more formal or more process-oriented than simple daję (I give).

So przekazuję bluzkę is not just I give the blouse in a casual sense; it can suggest I pass it along / hand it over to someone.

Yes. This is about aspect as well as tense.

• przekazuję = imperfective present
• przekażę = perfective future

Przekazuję can mean:

• I am handing it over
• I hand it over
• I hand it over whenever... (habitual)

So in this sentence it can sound like a general rule or repeated action: I hand over the blouse only when there is no stain.

If you said przekażę, it would usually mean one future completed action:

• Przekażę bluzkę tylko wtedy, gdy nie będzie plamy
  = I will hand over the blouse only if/when there is no stain

It literally means something like only then, when, but in natural English it is usually:

• only when
• only if

It introduces a condition:

• tylko wtedy, gdy nie ma plamy = only when/if there is no stain

You can think of tylko wtedy, gdy as a fixed pattern that is very common in Polish.

Sometimes, yes, but the nuance changes slightly.

• gdy = when
• kiedy = when
• jeśli = if

In many sentences, gdy and kiedy are interchangeable. Jeśli sounds more purely conditional.

So these are all possible in many contexts:

• tylko wtedy, gdy nie ma plamy
• tylko wtedy, kiedy nie ma plamy
• tylko jeśli nie ma plamy

The original version is very standard and natural.

Because gdy introduces a subordinate clause, and Polish normally separates subordinate clauses with a comma.

So:

• Przekazuję bluzkę z aksamitu, gdy...
• Przekazuję bluzkę z aksamitu tylko wtedy, gdy...

This is a regular Polish punctuation rule, not something special about this sentence only.

In Polish, negative existence is very often expressed with nie ma.

So:

• jest plama = there is a stain
• nie ma plamy = there is no stain

This is one of the most important patterns in Polish. English uses there is / there isn't, but Polish often uses jest / nie ma.

In this sentence, Polish does not explicitly say on the blouse, because the context makes it clear. If you wanted to be more explicit, you could say:

• gdy na bluzce nie ma plamy = when there is no stain on the blouse

Because after nie ma, Polish uses the genitive.

So:

• plama = nominative singular
• plamy = genitive singular

That is why the sentence says:

• nie ma plamy

not

• nie ma plama

This is a very common rule in Polish:

• jest problem → nie ma problemu
• jest kobieta → nie ma kobiety
• jest plama → nie ma plamy

Yes. Polish word order is more flexible than English because the case endings show the grammatical roles.

The original sentence is fine, but other orders are also possible:

• Bluzkę z aksamitu przekazuję tylko wtedy, gdy nie ma plamy.
• Tylko wtedy przekazuję bluzkę z aksamitu, gdy nie ma plamy.

The basic meaning stays similar, but the emphasis changes:

• starting with bluzkę z aksamitu puts more focus on the blouse
• starting with tylko wtedy puts more focus on the condition

A rough English-friendly approximation is:

• gdy ≈ g-dih

  • one syllable
  • no extra vowel between g and d
  • the y is not exactly an English sound, but ih is a useful approximation

• przekazuję ≈ pshe-ka-ZU-yeh

  • stress on ZU
  • rz here sounds like zh (like the s in measure)
  • the final -ję is roughly -yeh

These are only approximations, but they are enough to get you close.