Je préfère celles-ci parce qu’elles sont plus confortables.

Celles-ci is a demonstrative pronoun. It means these ones and replaces a noun that has already been mentioned or is obvious from context.

• ces = these/those
  • a noun
    
    • example: ces chaussures = these shoes
• celles-ci = these ones
  
  • it replaces the noun instead of repeating it

So if you are comparing two sets of shoes, you might say:

• Je préfère ces chaussures. = I prefer these shoes.
• Je préfère celles-ci. = I prefer these ones.

Elles just means they, so it would not have the same pointing/contrasting effect as celles-ci.

Because celles-ci is the feminine plural form, while ceux-ci is the masculine plural form.

The demonstrative pronouns are:

• celui-ci = this one / the latter one here (masculine singular)
• celle-ci = this one (feminine singular)
• ceux-ci = these ones (masculine plural)
• celles-ci = these ones (feminine plural)

So the form depends on the noun being replaced.

For example:

• les pantalons → ceux-ci
• les chaussures → celles-ci

-ci helps indicate this/these here, often in contrast with -là, which means that/those there.

So:

• celles-ci = these ones / these here
• celles-là = those ones / those there

In real modern French, people do not always make a strong physical distinction between -ci and -là, but the contrast is still common when choosing between items.

For example:

• Je préfère celles-ci, pas celles-là.
  = I prefer these ones, not those ones.

Because French usually shortens que to qu’ before a word starting with a vowel or a silent h. This is called elision.

So:

• parce que elles sont... → incorrect
• parce qu’elles sont... → correct

This happens very often in French:

• que il → qu’il
• que elle → qu’elle
• que on → qu’on

It makes pronunciation smoother.

Elles means they, and here it refers back to celles-ci.

Since celles-ci stands for a feminine plural noun, the matching subject pronoun is elles.

So the sentence structure is:

• Je préfère celles-ci = I prefer these ones
• parce qu’elles sont plus confortables = because they are more comfortable

French repeats the idea with elles in the second clause instead of leaving it implied.

Because the subject is plural: celles-ci / elles = these ones / they.

So:

• elles sont = they are
  (sont is the plural form of être)
• confortables gets an -s because adjectives usually agree with the noun/pronoun they describe in number and often in gender

Here, the hidden noun is feminine plural, so confortables is plural too.

A useful comparison:

• Elle est confortable. = It/she is comfortable.
• Elles sont confortables. = They are comfortable.

Yes. Here plus means more.

So:

• confortable = comfortable
• plus confortable = more comfortable
• plus confortables = more comfortable, agreeing with a plural noun/pronoun

French often forms the comparative with:

plus + adjective

Examples:

• plus grand = taller / bigger
• plus cher = more expensive
• plus confortable = more comfortable

In this sentence, the comparison is understood from context: these ones are more comfortable than the other ones.

The verb is préférer = to prefer. In the sentence, préfère is the first-person singular present tense form: I prefer.

French spelling keeps the accent marks because they affect pronunciation and are part of the correct written form.

Present tense:

• je préfère
• tu préfères
• il/elle préfère
• nous préférons
• vous préférez
• ils/elles préfèrent

Notice that the accent pattern changes in some forms. This is normal for this type of verb.

Yes, but it would change the meaning.

• Je préfère celles-ci = I prefer these ones
• Je préfère celles-là = I prefer those ones

So you choose -ci or -là depending on which items you are pointing to or contrasting.

If you are holding one pair of shoes and looking at another pair farther away, you might use one or the other accordingly.

Yes, that is possible in the right context, but it means something slightly different in emphasis.

• Je préfère celles-ci... strongly points out these ones
• Je les préfère... means I prefer them, so it depends more on context and does not by itself create the same this pair rather than that pair contrast

So if you are choosing between visible options, celles-ci is often clearer and more natural.

A careful pronunciation would be approximately:

zhuh pray-FEHR sel-see parsk-EL sohn ploos kohn-for-tab-luh

A few useful notes:

• Je sounds like zhuh
• préfère has stress-like emphasis for English learners on the second syllable
• celles-ci sounds roughly like sel-see
• qu’elles sounds like kel
• sont is nasal: roughly sohn
• In normal speech, plus before an adjective is often pronounced ploo
• confortables is roughly kohn-for-tab-luh

The exact sounds are different from English, but those approximations can help you get started.