Learn Hardcore Spanish (Latin America): Compré jamón para los sándwiches y también pepino para la ensalada. - I bought ham for the sandwiches and also cucumber for the salad.

Compré is the first-person singular of the preterite tense (past simple) of comprar. It’s used for completed actions in the past: I bought (and that’s it, it’s done).
In most of Latin America, the preterite is the normal choice even for very recent past actions. He comprado (present perfect: I have bought) is much more common in Spain; in Latin America you would still usually say compré jamón even if it was earlier today. Both are grammatically correct, but compré sounds more natural in Latin American Spanish in this context.

Why is there no yo in Compré jamón…? How do we know it means I bought?

Spanish usually drops subject pronouns because the verb ending already shows who the subject is.
The -é ending in compré clearly indicates first person singular (yo). Adding yo (Yo compré jamón…) is possible, but it’s only used for emphasis or contrast, like: Yo compré jamón, no tú (I bought ham, not you). In neutral, everyday speech, Compré jamón… is the natural form.

Why is there no article before jamón or pepino? Why not el jamón or un pepino?

Here jamón and pepino are used like uncountable or unspecified ingredients: I bought ham, (some) cucumber…
In Spanish, when you talk about buying an unspecified amount of a food/ingredient, you often omit the article: compré pan, leche, jamón, pepino.
If you say un pepino, it emphasizes one whole cucumber. El jamón would refer to a specific ham already known in the conversation, like the ham you had talked about before.

Why do we say para los sándwiches but just jamón (without any article)?

Jamón in this sentence is treated as an ingredient in general, so it doesn’t need an article: I bought ham.
Los sándwiches, with los, means the sandwiches that both speakers already know about (for example, the sandwiches you’re planning for a picnic or lunch).
So the structure is: I bought ham for the sandwiches — the sandwiches are specific; the ham is just “some ham.”

Why is para used instead of por in para los sándwiches and para la ensalada?

Para is used to express purpose or intended use: for the sandwiches, for the salad.
Por usually expresses cause, reason, duration, exchange, route, etc., and would be incorrect here.
So para los sándwiches / para la ensalada means with the purpose of using it in the sandwiches / salad.

Why is it los sándwiches but la ensalada? How do the genders work here?

Sándwich is masculine: el sándwich, los sándwiches.
Ensalada is feminine: la ensalada, las ensaladas.

Grammatical gender in Spanish is mostly arbitrary and must be learned word by word. The important part is that the article matches the noun: el / los for masculine, la / las for feminine. In this sentence, we have plural masculine (los sándwiches) and singular feminine (la ensalada).

Why is pepino singular? Does compré pepino mean “I bought one cucumber” or “I bought cucumber (in general)”?

Compré pepino most naturally suggests I bought (one) cucumber, because pepino is a countable noun.
However, in casual speech, if the context is not focused on number, it can just mean you bought cucumber as an ingredient, without stressing how many.
If you clearly want to say more than one, you’d normally say compré unos pepinos or compré varios pepinos (I bought some/several cucumbers).

Why is también placed before pepino? Could it go in a different position?

También usually goes before the word or phrase it modifies, especially before verbs or nouns: también pepino, también compré pepino.
You could also say:

También compré pepino para la ensalada.
Compré jamón y pepino también para la ensalada. (here it modifies the whole second phrase)

The original …y también pepino para la ensalada is very natural: it adds pepino as an extra item to the list of things you bought.

Why do we say para la ensalada and not just para ensalada?

Para la ensalada usually refers to a specific salad the speakers have in mind (today’s salad, the salad for dinner, etc.).
Para ensalada (without article) can mean “for salad in general” (for use in salads, as a type of ingredient), but it sounds less common and more generic.
In everyday conversation, when you’re clearly talking about a particular meal, para la ensalada is the normal choice.

Why is the plural sándwiches and not something like sándwichs or sandwiches?

The standard Spanish plural of sándwich is sándwiches: you add -es to a noun ending in a consonant.
The accent stays on the same syllable: SÁN-dwich / SÁN-dwich-es.
In Latin America, there are also regional alternatives like sánduche, sánguche, sangüiche, etc., but in neutral, general Spanish sándwich / sándwiches is the usual form.

What do the accent marks in compré, sándwiches, and también do?

The written accents show where the stress falls in the word:

compré is stressed on -pré (com-PRÉ), not COM-pre.
sándwiches is stressed on SÁN (SÁN-dwi-ches).
también is stressed on -bién (tam-BIÉN).

Without these accents, the pronunciation and sometimes the meaning could change, so they’re essential in standard Spanish spelling.

Can the word order of the sentence change? For example, can I start with También compré pepino…?

Yes, Spanish word order is fairly flexible as long as the relationships are clear. Some natural alternatives are:

También compré jamón para los sándwiches y pepino para la ensalada.
Compré jamón para los sándwiches y pepino también para la ensalada.

The original order Compré jamón… y también pepino… emphasizes that pepino is an additional item you bought, on top of the ham.