El telón y la puesta en escena cambian.

Because the subject is plural: El telón y la puesta en escena = the curtain and the staging.
When two singular nouns are joined by y (and), they normally make a plural subject, so the verb must be plural too.

• el telón cambia = the curtain changes
• la puesta en escena cambia = the staging changes
• el telón y la puesta en escena cambian = the curtain and the staging change

Puesta en escena is a set phrase often used in theatre, film, and the arts. It refers to the staging, presentation, or mise-en-scène of a performance: how things are arranged visually on stage or on screen.

Grammatically, it works as a feminine singular noun phrase:

• la puesta en escena

Even though it contains several words, it behaves like one unit.

In Spanish, articles such as el, la, los, and las are often used more regularly than in English.
Here, la is needed because puesta en escena is a specific noun phrase and it is the subject of the sentence.

So Spanish naturally says:

• El telón y la puesta en escena cambian.

Where English might sometimes omit an article in a more general statement, Spanish often keeps it.

Because these are two separate nouns, and each one has its own gender and article:

• el telón = masculine singular
• la puesta en escena = feminine singular

Spanish usually repeats the article before each noun when listing them, especially when they are separate items.

Telón usually means curtain, especially a stage curtain in a theatre.
It is a masculine noun:

• el telón
• plural: los telones

In this sentence, it most likely refers to the theatrical curtain, not an ordinary household curtain.

Y means and. It links the two subjects:

• el telón
• la puesta en escena

So: el telón y la puesta en escena = the curtain and the staging

A useful extra point: y changes to e before words beginning with an i sound.

For example:

• padre e hijo = father and son

But here it stays y because la puesta does not begin with that sound.

Yes. Cambian is the third person plural present of cambiar (to change).

Present-tense forms of cambiar:

• yo cambio
• tú cambias
• él/ella cambia
• nosotros cambiamos
• vosotros cambiáis
• ellos/ellas cambian

Here, cambian matches the plural subject el telón y la puesta en escena.

Yes, but it means something slightly different.

• cambian = they change / are changing (general present, broad statement, or habitual/action in context)
• están cambiando = they are changing (right now, in progress)

So:

• El telón y la puesta en escena cambian.
  More neutral or general.

• El telón y la puesta en escena están cambiando.
  Emphasises that the change is happening at this moment.

A rough Spain-Spanish pronunciation guide:

• telón ≈ teh-LON
• puesta en escena ≈ PWEHS-ta en es-THE-na in much of Spain
  or es-SE-na in Latin America and some speakers

A few details:

• The stress in telón falls on the last syllable because of the written accent: -lón
• In most of Spain, c before e is pronounced like the th in think, so escena sounds like es-THE-na
• pu in puesta sounds like pweh

Because Spanish often leaves subject pronouns out when they are not needed. The verb ending already shows the person and number.

• cambian already tells you the subject is they or you all (depending on context)
• Here, the actual subject is stated explicitly: El telón y la puesta en escena

So adding ellos would usually be unnecessary.

Yes, Spanish word order is often more flexible than English, but the usual order here is very natural:

• El telón y la puesta en escena cambian.

You could rearrange it for emphasis in some contexts:

• Cambian el telón y la puesta en escena.

But that sounds more marked or literary, and in many situations the original version is the most straightforward.

Yes. Cambiar can mean:

• to change
• to alter
• sometimes to replace or to switch, depending on context

In this sentence, without more context, the most natural idea is that the curtain and the staging change or are changing. The exact nuance depends on what was happening before and after in the text.

Yes, very likely. Both telón and puesta en escena strongly suggest a theatrical or performance context.

• telón = stage curtain
• puesta en escena = staging / scenic presentation

So a learner would naturally read this as something connected to theatre, opera, performance, or possibly film/art criticism.