Frater et soror saepe contendunt, sed mater pacem servare vult.

Because frater et soror is a compound subject: brother and sister together make two people, so the verb must be 3rd person plural.

• frater = brother
• soror = sister
• contendunt = they argue / they struggle / they contend

So Latin works like English here: The brother and sister argue, not argues.

Contendunt is the present active indicative, 3rd person plural of contendere.

That tells you:

• present = happening now or generally
• active = the subject does the action
• indicative = ordinary statement
• 3rd person plural = they

The ending -unt is a common sign of 3rd person plural present for many 3rd-conjugation verbs.

Because pacem is the accusative singular form of pax.

• pax = nominative singular, usually used for the subject
• pacem = accusative singular, used for the direct object

In this sentence, peace is the thing the mother wants to preserve, so it is the direct object of servare. Therefore Latin uses pacem.

Because it depends on vult.

Vult means wants, and in Latin verbs like volo often take an infinitive to show what someone wants to do.

So:

• vult = she wants
• servare = to preserve / to keep

Together: vult servare = she wants to preserve

This is very similar to English wants to preserve.

Because Latin usually expresses that idea with the infinitive form itself.

So English needs two words:

• to preserve

But Latin uses one word:

• servare

The -are ending shows it is an infinitive.

Mater is nominative singular because it is the subject of vult.

In the second clause:

• mater = mother
• vult = wants

So mother is the person doing the wanting, which makes it the subject.

By itself, vult means he/she/it wants. The verb form does not tell you the gender.

You know it means she wants here because the subject is mater, a feminine noun meaning mother.

So:

• vult = he/she/it wants
• mater vult = the mother wants, so in English: she wants

Saepe is an adverb meaning often. It modifies the verb contendunt.

So:

• frater et soror saepe contendunt = the brother and sister often argue

Latin adverbs are often fairly flexible in position, but placing saepe near the verb is very common and clear.

Yes. Latin word order is much more flexible than English because the endings show how the words function.

This sentence could be rearranged in different ways and still mean basically the same thing, for example:

• Mater pacem servare vult, sed frater et soror saepe contendunt.
• Frater et soror contendunt saepe, sed mater pacem servare vult.

The exact word order can change the emphasis, but the grammatical relationships are still shown mainly by the endings:

• mater = subject
• pacem = object
• contendunt = plural verb
• vult = singular verb

Classical Latin does not have definite or indefinite articles.

So:

• frater can mean brother, a brother, or the brother
• mater can mean mother, a mother, or the mother

You decide from context which English article sounds best.

Sed is a conjunction meaning but. It connects the two clauses and shows a contrast:

• Frater et soror saepe contendunt = the brother and sister often argue
• sed mater pacem servare vult = but the mother wants to preserve peace

So sed signals that the second idea contrasts with the first.

The usual dictionary forms are:

• frater, fratris = brother
• soror, sororis = sister
• mater, matris = mother
• pax, pacis = peace
• contendo, contendere, contendi, contentum = strive, contend, argue
• servo, servare, servavi, servatum = preserve, keep
• volo, velle, volui = want

For a learner, it is especially useful to notice that pax becomes pacem in the accusative, and that volo is an irregular verb.

Yes. They are all 3rd-declension nouns, though they do not all look exactly the same in every form.

Their nominative singular forms are:

• frater
• soror
• mater
• pax

A learner often notices that 3rd-declension nouns can have quite varied nominative forms, so it is important to learn the genitive singular too:

• fratris
• sororis
• matris
• pacis

That genitive form helps you see the stem more clearly.

It depends on context. Servare can mean several related things, such as:

• to save
• to preserve
• to keep
• to maintain

In pacem servare, the most natural English choices are usually:

• to preserve peace
• to keep the peace
• to maintain peace

So the exact English wording can vary even though the Latin is the same.

A simple classroom pronunciation would be something like:

FRAH-ter et SO-ror SAI-peh con-TEN-doont, sed MA-ter PA-kem ser-WAH-reh woolt.

A few helpful points:

• c in Classical Latin is always hard, like k
• v in reconstructed Classical pronunciation is closer to w
• ae is often pronounced like eye in Classical pronunciation
• pacem begins with a p sound, and the c is hard: PA-kem

Pronunciation traditions differ, but these basics will help a lot.