La lanzadera gira bajo la placa de aguja.

Because both nouns are feminine singular, so they take the feminine singular definite article la.

• la lanzadera = the shuttle
• la placa = the plate

In Spanish, articles are used very often, even in technical descriptions where English might sometimes drop them.

Gira is the third-person singular present tense of girar.

• girar = to turn / to rotate
• gira = it turns / it rotates

It matches la lanzadera, which is a singular noun. Spanish often uses the simple present for descriptions, instructions, and how machines work, so gira is very natural here.

Spanish can use está girando for is turning, but in technical descriptions the simple present is usually more natural:

• La lanzadera gira... = neutral, general description
• La lanzadera está girando... = emphasizes that it is turning right now

In manuals, explanations, and general statements, Spanish often prefers the simple present where English might use either simple present or present continuous.

Here bajo means under / beneath.

So:

• bajo la placa de aguja = under the needle plate

Yes, debajo de could also work:

• La lanzadera gira debajo de la placa de aguja.

That sounds a little more explicit and conversational. Bajo is slightly more compact and often sounds good in technical or written descriptions.

Spanish usually links two nouns with de where English often puts one noun directly before another.

So:

• placa de aguja = literally plate of needle
• natural English = needle plate

This noun + de + noun pattern is extremely common in Spanish:

• caja de herramientas = tool box
• motor de gasolina = petrol engine / gasoline engine

In a phrase like placa de aguja, the second noun often appears without an article because it functions more like a classifier or type label.

So de aguja means something like for the needle / relating to the needle, not of the needle in a very literal sense.

Compare:

• la placa de aguja = the needle plate
• la placa de la aguja = would sound more like the plate of the needle, referring to a specific needle, which is usually not what is meant

It is a real Spanish word, but in this sentence it is being used in a technical sewing-machine sense.

Depending on context, lanzadera can mean different things, including:

• shuttle in sewing or weaving
• space shuttle in other contexts

So the exact meaning depends on the topic. Here, because of placa de aguja, it clearly belongs to sewing-machine vocabulary.

Yes. This is the most neutral and natural order:

• La lanzadera = subject
• gira = verb
• bajo la placa de aguja = location

So the structure is:

Subject + Verb + Place

Spanish is flexible with word order, but this version is the standard, straightforward way to say it.

In Spain Spanish:

• gira is pronounced roughly HEE-ra
• aguja is pronounced roughly ah-GOO-ha

Important point: the g before i in gira, and the j in aguja, both make a strong throaty sound in Spanish from Spain, not a hard English g sound.

So:

• gira does not sound like English geera
• aguja does not sound like agoo-ja

Yes. Both are possible.

• turns sounds more everyday and general
• rotates sounds more technical or mechanical

Since this sentence is about a machine part, rotates may fit the context very well, but turns is also correct.

Yes. Bajo can be:

• a preposition: under / beneath
• an adjective: low / short
• a noun in music: bass

But in this sentence it is clearly the preposition meaning under:

• bajo la placa de aguja = under the needle plate