Puse rábano y pepinillo en la ensalada.

Because poner is an irregular verb in the preterite.

The infinitive is poner = to put.
Its preterite forms are:

• yo puse
• tú pusiste
• él/ella/usted puso
• nosotros pusimos
• vosotros pusisteis
• ellos/ellas/ustedes pusieron

So puse means I put.

This is a very common pattern in Spanish: some high-frequency verbs have irregular preterite stems. For poner, the stem changes to pus-.

Spanish often drops subject pronouns when they are not needed.

So:

• Puse rábano y pepinillo en la ensalada.
• Yo puse rábano y pepinillo en la ensalada.

Both mean I put radish and gherkin/pickle in the salad.

The yo is usually omitted because puse already tells you the subject is I.
You would add yo only for emphasis, contrast, or clarity, for example:

• Yo puse el pepinillo, no tú.
  I put in the gherkin, not you.

In this sentence, puse most naturally means I put or I added.

With food, poner is very often used in Spanish where English might prefer add:

• Puse sal. = I added salt.
• Puse tomate en la ensalada. = I put / added tomato in the salad.

So while the literal meaning is I put, a natural English translation in context may be I added.

Because Spanish often leaves out the article when talking about ingredients, materials, or unspecified amounts.

So:

• Puse rábano y pepinillo en la ensalada.

sounds like:

• I added radish and gherkin/pickle to the salad.

It is not necessarily referring to specific, already-known radishes and pickles.

If you said:

• Puse el rábano y el pepinillo en la ensalada

that would sound more like you mean the specific radish and the specific gherkin already mentioned or identifiable from context.

Because in Spanish, singular nouns are often used to refer to an ingredient or food item in a general/uncountable way, similar to English:

• Lleva tomate. = It has tomato.
• Añadí cebolla. = I added onion.

So rábano y pepinillo can mean radish and gherkin/pickle as ingredients in general, not necessarily exactly one of each.

If you wanted to emphasise multiple pieces or several items, you could use the plural:

• Puse rábanos y pepinillos en la ensalada.

That would suggest radishes and gherkins/pickles more explicitly as countable items.

In Spain, pepinillo usually means a small cucumber, and very often specifically a pickled gherkin.

So in a sentence like this, many learners would naturally interpret it as:

• gherkin
• pickle
  depending on the English variety and context.

A few related words:

• pepino = cucumber
• pepinillo = small cucumber / gherkin, often pickled

In food contexts in Spain, pepinillo often brings to mind the pickled kind.

Because poner algo en algo is the normal structure for putting something into something.

• Puse rábano y pepinillo en la ensalada.
  I put / added radish and gherkin in(to) the salad.

Here, en marks the place/container/resulting location.

Using a would not be the normal choice with poner in this sentence.

Compare:

• Puse azúcar en el café. = I put sugar in the coffee.
• Puse hielo en el vaso. = I put ice in the glass.

The accent mark shows where the stress goes.

• rábano is stressed on the first syllable: RA-ba-no

Without the accent, Spanish spelling rules would suggest a different stress pattern, so the written accent is needed.

This is useful for pronunciation and also for recognising the word correctly.

Spanish normally uses y for and:

• rábano y pepinillo

It changes to e only before words that begin with an i sound:

• padre e hijo
• España e Italia

Since pepinillo begins with a p sound, you keep y.

In Spain Spanish, both are possible, but they can suggest slightly different time frames.

• Puse... = preterite; often used for a completed action in the past
• He puesto... = present perfect; often used in Spain for a recent past action connected to the present

So:

• Puse rábano y pepinillo en la ensalada.
  sounds like a simple completed past action.
• He puesto rábano y pepinillo en la ensalada.
  can sound more like I’ve put radish and gherkin in the salad / I just added them.

In many contexts in Spain, the present perfect is especially common for something done today or just now, but the preterite is also very common and perfectly correct depending on region and context.

Yes. That is also correct and often very natural.

• Puse rábano y pepinillo en la ensalada.
• Añadí rábano y pepinillo a la ensalada.

Both can mean I added radish and gherkin/pickle to the salad.

The difference is mainly one of verb choice:

• poner = to put
• añadir = to add

With food, both are common, but añadir sounds a little more explicitly like adding an ingredient, while poner is very everyday and conversational.

The structure is:

• Puse = verb
• rábano y pepinillo = direct object
• en la ensalada = prepositional phrase showing where they were put

So the pattern is:

[verb] + [thing added] + en + [place/container]

A few similar examples:

• Puse sal en la sopa.
• Puse queso en la pasta.
• Puse hielo en la bebida.

This makes Puse rábano y pepinillo en la ensalada a very typical Spanish sentence pattern.