Mi padre apretó una tuerca del somier con un alicate y dejó el cabecero bien sujeto.

Apretó comes from the infinitive apretar.

Here it means tightened:

• apretar una tuerca = to tighten a nut

More generally, apretar can also mean:

• to squeeze
• to press
• to tighten

So it is a very common verb with both literal and figurative uses.

They are in the preterite because the sentence describes completed actions in the past:

• apretó = he tightened
• dejó = he left

The speaker is telling us what happened as a finished sequence:

1. he tightened the nut
2. he left the headboard securely fixed

If the sentence used the imperfect, it would suggest something ongoing, habitual, or backgrounded, which would not fit as well here.

The accent mark shows that the stress falls on the last syllable:

• apretó
• dejó

It also helps distinguish these forms from other verb forms. In practice, when you see a verb ending in -ó, it is very often the third-person singular preterite:

• habló = he/she spoke
• miró = he/she looked
• dejó = he/she left

In Spain, somier usually refers to the bed base that supports the mattress, often a slatted base.

So it is not the mattress itself. It is the structure underneath it.

Depending on context, English translations might include:

• bed base
• slatted bed base
• sometimes bed frame, if the distinction is not important

Because de + el contracts to del in Spanish.

So:

• de el somier → del somier

This is standard and compulsory in normal Spanish, except with certain proper names.

Here una tuerca del somier means:

• a nut from/on/of the bed base
• in other words, a nut that belongs to that part of the bed

Alicate refers to a tool like pliers.

This is a good vocabulary point because English usually says pliers in the plural, while Spanish can use:

• un alicate
• or unos alicates

In everyday Spanish, alicates is very common, but the singular alicate also exists and is understood.

So con un alicate means with a pair of pliers / with a plier-like tool.

Cabecero means headboard.

It is the part at the head of the bed, not the whole bed.

In Spain, cabecero is the normal everyday word for this piece of furniture.

Literally, it is something like:

he left the headboard well secured

This is a very common Spanish pattern:

dejar + object + adjective/past participle

It means to leave something in a certain state.

Examples:

• dejó la puerta abierta = he left the door open
• dejó la mesa limpia = he left the table clean
• dejó el cabecero bien sujeto = he left the headboard securely fastened

So dejó here does not just mean left in the sense of went away from; it means left it in that condition.

Here sujeto means secured, fastened, or held firmly in place.

It comes from sujetar = to hold, to secure, to fasten.

So:

• bien sujeto = well secured
• mal sujeto = badly secured / loose

In this sentence, sujeto works like an adjective describing the state of the headboard after the action.

Because bien sujeto is the natural idiomatic way to say securely fastened or firmly attached.

Here bien does not simply mean well in a moral sense; it means something like:

• properly
• securely
• firmly

So:

• bien sujeto = securely fixed
• muy sujeto would sound less natural here

Spanish often uses bien + past participle/adjective in this way:

• bien cerrado = tightly closed
• bien atado = tightly tied
• bien sujeto = firmly secured

Because una tuerca introduces it as one nut or a nut, without assuming the listener already knows which one.

Use la tuerca if it is a specific, already identified nut:

• Mi padre apretó la tuerca del somier = he tightened the nut on the bed base

Use una tuerca if you are just mentioning one of them:

• Mi padre apretó una tuerca del somier = he tightened a nut on the bed base

Both are possible, but they give slightly different information.

Yes. Apretar is very common for tightening all sorts of things, especially in everyday language.

Examples:

• apretar un tornillo = to tighten a screw
• apretar una tuerca = to tighten a nut
• apretar los cordones = to tighten the laces

So if you are talking about making something physically tighter, apretar is often a good choice.