Learn Hardcore Polish: Oferta, którą dostałem w internecie, obejmuje także bezpłatny parasol. - The offer that I got on the internet also includes a free umbrella.

którą is the relative pronoun który in the feminine singular accusative form. We use it because it refers to oferta (a feminine noun) and functions as the direct object of dostałem. In Polish, relative pronouns must agree in gender, number, and case with the noun they refer to.

Why is it w internecie and not na internecie?

Polish typically treats the Internet as a space you’re “in,” so the standard preposition is w: w internecie (in the Internet).

na internecie occurs colloquially but is less standard.
You can also say przez internet (via the Internet) when you want to emphasize the channel of communication.

Can I use przez internet instead of w internecie, and is there any difference?

Yes.

w internecie emphasizes location (“in the Internet”).
przez internet emphasizes means or channel (“through the Internet”).
Both are correct and commonly used, so choose based on whether you think of the Internet as a place or a medium.

What case is bezpłatny parasol in? Why does parasol look like the nominative?

Here parasol is the direct object of obejmuje, so it’s in the accusative case. Masculine inanimate nouns (like parasol) have identical forms in the nominative and accusative, which is why it appears unchanged.

Why is bezpłatny used? Why not wolny or za darmo?

bezpłatny is an adjective meaning “free of charge.”
wolny means “free” as in “not occupied” or “available,” so it wouldn’t convey “no cost.”
za darmo is an adverbial phrase (“for free”) and would require rephrasing, for example: Oferta… obejmuje parasol za darmo.

What’s the difference between także, też, and również?

All three translate as “also” or “too,” but differ in register:

też is the most colloquial and common in speech.
także is more neutral and often found in written Polish.
również is the most formal and typical in academic or official contexts.
They are largely interchangeable; pick one to match your level of formality.

Why are there commas around którą dostałem w internecie?

The commas enclose the relative clause którą dostałem w internecie because it provides additional (non-essential) information about oferta. In Polish, non-restrictive relative clauses are set off by commas to show they aren’t defining which specific item you mean but merely adding extra detail.

Could these commas be omitted? When do you use commas with który clauses?

You omit commas if the relative clause is essential to identify the noun (a restrictive clause). For example, if you have several offers and only the one you received online includes the umbrella, you might write:
Oferta którą dostałem w internecie obejmuje bezpłatny parasol.
General guideline:

Non-restrictive (extra info): use commas.
Restrictive (defines identity): no commas.
In everyday writing, commas are often used even with restrictive clauses, but the distinction exists.

Why aren’t there articles like the or a in this sentence?

Polish has no articles. Definiteness and indefiniteness are conveyed through context, word order, or additional words (e.g., jakąś for “some/a certain”). Here oferta can mean “an offer” or “the offer” purely from context.