Solo necesito una cucharada de aceite para esta ensalada.

Putting solo first emphasizes only / just. In this sentence, it highlights that the amount needed is small.

Spanish word order is fairly flexible, so these are also possible:

• Solo necesito una cucharada de aceite para esta ensalada.
• Necesito solo una cucharada de aceite para esta ensalada.
• Para esta ensalada, solo necesito una cucharada de aceite.

They all mean basically the same thing, but the first one sounds very natural and emphasizes only right away.

Usually, no. Modern standard Spanish normally writes solo without an accent, whether it means alone or only.

Older rules and some writers used sólo for only to avoid ambiguity, but in current standard usage solo is the normal spelling.

So in this sentence, Solo necesito... is the standard modern form.

Spanish often leaves out subject pronouns because the verb ending already shows who the subject is.

• necesito = I need
• necesitas = you need
• necesita = he/she/it needs or you formal need

So yo is not necessary here. You could say Yo solo necesito una cucharada..., but that adds emphasis, as if you were contrasting yourself with someone else.

Necesito is the first person singular present tense of necesitar.

Present tense forms:

• yo necesito
• tú necesitas
• él / ella / usted necesita
• nosotros / nosotras necesitamos
• vosotros / vosotras necesitáis
• ellos / ellas / ustedes necesitan

In the sentence, necesito means I need.

Cuchara means spoon.

Cucharada means a spoonful / tablespoonful. It refers to the amount that fits in a spoon, not just the object itself.

So:

• una cuchara = a spoon
• una cucharada = a spoonful / tablespoon

Very often in cooking, una cucharada is understood as a tablespoon.

You may also see:

• una cucharadita = a teaspoon
• una cucharada sopera = a tablespoon, more explicitly

After a quantity or measure word in Spanish, you usually use de before the substance or thing being measured.

So:

• una cucharada de aceite = a spoonful of oil
• un vaso de agua = a glass of water
• un kilo de arroz = a kilo of rice

This is a very common structure:

quantity/measure + de + noun

Because after a measure expression like una cucharada de..., Spanish normally uses the bare noun:

• una cucharada de aceite
• un poco de azúcar
• un vaso de leche

You would not normally say una cucharada del aceite unless you mean a spoonful of the oil from some specific oil already mentioned.

Compare:

• una cucharada de aceite = a spoonful of oil
• una cucharada del aceite = a spoonful of the oil

Here para means for, expressing purpose or intended use.

• para esta ensalada = for this salad

You are saying the oil is needed for the purpose of making or dressing this salad.

Por would not sound right here. Por is used for meanings like because of, through, by, for the sake of, etc., but not for this kind of intended use.

Ensalada is a feminine singular noun, so the demonstrative has to match it:

• este for masculine singular
• esta for feminine singular

Examples:

• este libro = this book
• esta ensalada = this salad

So esta agrees with ensalada in gender and number.

Both mean a kind of that/this salad, but the choice depends on how close the speaker feels the thing is.

• esta ensalada = this salad, usually something near the speaker or mentally close
• esa ensalada = that salad, usually a bit farther away or less immediate

In many everyday situations, esta is used when talking about the salad right in front of you or the one you are currently making.

Yes. Solo and solamente both mean only / just here.

So this is also correct:

• Solamente necesito una cucharada de aceite para esta ensalada.

The difference is mostly style:

• solo is shorter and more common in everyday speech
• solamente can sound a little more explicit or slightly more formal

Yes. Spanish allows more flexibility than English, although some versions sound more natural than others.

Natural alternatives include:

• Para esta ensalada solo necesito una cucharada de aceite.
• Solo necesito una cucharada de aceite para esta ensalada.
• Necesito solo una cucharada de aceite para esta ensalada.

The original sentence is very natural. Reordering usually changes emphasis rather than basic meaning.

In most of Spain, aceite is pronounced roughly as a-they-te, because the c before e is pronounced like the th in think:

• aceite → a-THAY-te

More precisely, the stress is on the second syllable:

• a-CEI-te

In many parts of Latin America, that c is pronounced like s, so it sounds more like a-SAY-te.

Both are correct in their respective varieties, but for Spain the th sound is the usual model.