El carrete queda sobre el portacarretes.

In this sentence, quedar means something like to end up / to be left / to sit / to be positioned. It often sounds natural when describing where something is placed or where it is supposed to go.

So El carrete queda sobre el portacarretes suggests the spool sits/goes on top of the spool holder.

If you used está, the sentence would simply describe location: the spool is on the spool holder.
With queda, there is often a slight idea of resulting position or proper placement.

Because the subject is El carrete, which is singular.

• El carrete = the spool
• queda = third person singular of quedar

If the subject were plural, you would use quedan:

• Los carretes quedan sobre el portacarretes.

Here, sobre means on / on top of / over.

In this sentence, it indicates physical position: the spool is on top of the spool holder.

Spanish often uses:

• sobre = on, over
• encima de = on top of
• en = in, on, at

In this specific sentence, sobre is a natural choice because it clearly expresses that one object is physically resting above another.

Yes, very often you could.

• El carrete queda sobre el portacarretes.
• El carrete queda encima del portacarretes.

Both can mean roughly the same thing here.

A small difference:

• sobre is often a bit more neutral or slightly more formal
• encima de strongly emphasizes on top of

Also note the contraction:

• de + el = del

So encima del portacarretes = on top of the spool holder

Portacarretes is a compound noun.

It is built from:

• porta- = holder / carrier / something that holds
• carretes = spools

So portacarretes literally means spool-holder.

Spanish has many similar compound words with porta-, for example:

• portaequipajes = luggage rack
• portavasos = cup holder
• portarrollos = roll holder

These words are very common in technical or everyday object names.

Because some Spanish compound nouns have a form that looks plural but can be singular in meaning.

So:

• el portacarretes = the spool holder
• los portacarretes = the spool holders

The word itself often stays the same, and the article tells you whether it is singular or plural.

This is very common with compound nouns like:

• el paraguas / los paraguas
• el portaequipajes / los portaequipajes

So in your sentence, el shows clearly that portacarretes is singular.

Because both carrete and portacarretes are masculine singular nouns in this sentence.

• el carrete
• el portacarretes

In Spanish, nouns normally need an article when you are talking about a specific object, especially in a full sentence like this one.

Here, both are:

• masculine
• singular
• definite (the)

So el is the correct article for both.

The rr in carrete is a rolled/trilled r, stronger than the English r.

A rough pronunciation guide:

• ca-rre-te

The rr is important because Spanish distinguishes:

• r = a softer tap sound
• rr = a stronger trill

For English speakers, this is one of the harder sounds to master. The key point is that rr is not pronounced like an English r.

Also, carrete is stressed on the middle syllable:

• ca-RRE-te

In this sentence, carrete means spool or reel.

But depending on context, carrete can have other meanings. For example, in some contexts it can refer to:

• a film roll
• a reel
• in some varieties of Spanish, even slang meanings

For a learner, the important thing is: in this sentence, it is the physical spool/reel that goes onto the portacarretes.

Yes, that is grammatically possible, but it sounds more marked or stylistically different.

The basic, neutral order is:

• El carrete queda sobre el portacarretes.

If you say:

• Sobre el portacarretes queda el carrete.

you are putting more focus on the location. This kind of word order might appear in instructions, descriptions, or more formal writing, but it is not the most neutral version.

For learners, the original order is the safest and most natural to produce.

Usually not in the same straightforward way.

• queda here means is positioned / sits / goes
• se queda usually means stays / remains

So:

• El carrete queda sobre el portacarretes. = The spool sits/goes on the spool holder.
• El carrete se queda sobre el portacarretes. = The spool stays on the spool holder.

The second version changes the meaning. It sounds like you are emphasizing that it remains there, not simply describing its position.

It can sound like either, depending on context.

It may describe:

• where the spool is
• where the spool belongs
• how the parts are arranged

Because quedar often suggests resulting position, the sentence can sound slightly instructional, especially in manuals or explanations of how a machine is assembled.

So in a technical context, it may feel close to:

• The spool goes on the spool holder.

That is one reason queda is a very natural choice here.

You could sometimes hear en, especially if the idea is more general, but sobre is more precise here.

• en = in / on / at
• sobre = on top of / over

Since a spool typically rests on top of a spool holder rather than being inside it, sobre gives a clearer mental image.

So sobre el portacarretes is the more exact phrasing for this situation.