Jeśli zrobię herbatę, postawię filiżankę na obrusie i położę obok serwetkę.

Because Polish usually leaves out subject pronouns when the verb ending already shows the subject.

In zrobię, postawię, and położę, the ending -ę means I. So Polish does not need ja here.

You could add ja for emphasis or contrast, for example: Jeśli ja zrobię herbatę...
This would sound more like If I’m the one who makes the tea...

These are perfective verbs. In Polish, perfective verbs do not normally have a true present tense. Their present-looking forms are used with future meaning.

So:

• zrobię = I will make / I will prepare
• postawię = I will place / I will set down
• położę = I will lay / I will put down

This is very common in Polish. English speakers often expect something like will, but Polish does not need a separate future word here.

That is just a difference between the two languages.

In English, after if, we usually use a present form for future meaning:

• If I make tea, I’ll...

In Polish, you can use the normal future meaning form in both parts:

• Jeśli zrobię herbatę, postawię...

So this is natural Polish, even though it does not match English grammar word-for-word.

Because the sentence describes single, completed actions:

• zrobię herbatę = I will make the tea
• postawię filiżankę = I will set the cup down
• położę serwetkę = I will place the napkin

The speaker is talking about doing each thing once, as a complete event.

If you used imperfective verbs, the meaning would shift toward:

• process
• repeated action
• ongoing action
• habitual action

For example, Jeśli będę robić herbatę... would mean more like If I am making tea..., not the same idea as this sentence.

Yes. It is very natural Polish.

Literally, zrobić often means to do / to make, but in this kind of context zrobić herbatę means to make / prepare tea.

You may also hear:

• zaparzyć herbatę = to brew tea

That is a bit more specific. But zrobić herbatę is a very common everyday expression.

Polish often distinguishes how something is placed.

• postawić means to set/stand something upright
• położyć means to lay something down, usually flat or horizontally

So here:

• a cup is something you normally stand/set down → postawię filiżankę
• a napkin is something you normally lay down → położę serwetkę

In English, put can cover both ideas, but Polish is often more specific.

Because they are in the accusative case, used here for direct objects.

The basic dictionary forms are:

• herbata → herbatę
• filiżanka → filiżankę
• serwetka → serwetkę

These are all feminine singular nouns, and in this pattern the accusative ending is -ę.

They are direct objects because they answer what?

• make what? → herbatę
• place what? → filiżankę
• lay what? → serwetkę

Because obrusie is the locative singular of obrus (tablecloth), and after na Polish often uses the locative to indicate the surface/location where something is placed.

So:

• obrus = tablecloth
• na obrusie = on the tablecloth

English speakers are often taught a simple rule that na + accusative is movement and na + locative is location. That rule helps, but real usage is a bit more nuanced. With verbs like postawić and położyć, Polish very often uses na + locative to express the place where the object ends up.

So postawię filiżankę na obrusie is natural Polish.

Here obok means something like next to it / beside it / nearby.

The sentence does not say explicitly next to what, because it is understood from context. Most naturally, it means next to the cup or next to the place setting.

Polish often leaves this kind of reference implicit if it is obvious.

Also, obok can work in two ways:

• as an adverb: obok = next to / beside / nearby
• with a noun: obok + genitive
  • obok filiżanki = next to the cup

So here the noun after obok is simply omitted.

Polish word order is fairly flexible, but different orders change the emphasis.

This version is neutral and natural: Jeśli zrobię herbatę, postawię filiżankę na obrusie i położę obok serwetkę.

You could also hear variations such as:

• Jeśli zrobię herbatę, położę obok serwetkę i postawię filiżankę na obrusie.
• Jeśli zrobię herbatę, postawię na obrusie filiżankę i położę obok serwetkę.

These are still understandable, but the focus shifts slightly. The original sentence sounds like a normal, straightforward way to say it.

Because Jeśli zrobię herbatę is a subordinate clause introduced by jeśli (if).

In Polish, subordinate clauses are separated by commas:

• Jeśli zrobię herbatę, postawię filiżankę...
• Postawię filiżankę..., jeśli zrobię herbatę.

So the comma is required here.

Yes. Jeśli and jeżeli both mean if.

In most situations they are interchangeable:

• Jeśli zrobię herbatę...
• Jeżeli zrobię herbatę...

Very roughly:

• jeśli is often a bit more common in everyday speech
• jeżeli can sound slightly more formal or careful

But both are correct and natural.