Paul tient l’échelle pendant que sa sœur examine la fissure dans le mur.

Tenir is the infinitive, meaning to hold. In the sentence, the verb has to be conjugated because the subject is Paul.

So:

• tenir = to hold
• il tient = he holds / he is holding

Since Paul is third-person singular, French uses tient:

• je tiens
• tu tiens
• il / elle tient
• nous tenons
• vous tenez
• ils / elles tiennent

So Paul tient l’échelle means Paul is holding the ladder.

Here, tenir means to hold or to keep steady.

So Paul tient l’échelle suggests that Paul is physically supporting the ladder so it stays in place while his sister looks at the crack.

This is a very common use of tenir:

• tenir une porte = hold a door
• tenir un sac = hold a bag
• tenir l’échelle = hold the ladder

French tenir can also have other meanings in other contexts, such as to keep, to maintain, or even parts of expressions, so context matters.

Because échelle is a feminine noun that begins with a vowel sound, la becomes l’ before it.

So:

• la table
• la fissure
• but l’échelle

This is called elision. French usually drops the vowel in le or la before a word beginning with a vowel or silent h.

That is why you get:

• l’échelle
• l’école
• l’amie

instead of la échelle, la école, etc.

Pendant que means while and is used before a clause with its own subject and verb.

Here the part after it is:

sa sœur examine la fissure dans le mur

That is a full clause, because it has:

• a subject: sa sœur
• a verb: examine

So French needs pendant que.

Compare:

• Paul tient l’échelle pendant que sa sœur examine la fissure.
  = Paul holds the ladder while his sister examines the crack.

But pendant by itself is usually used before a noun or time expression:

• pendant une heure = for an hour
• pendant la réunion = during the meeting

Because sœur is a feminine singular noun, so the correct possessive adjective is sa.

French possessive adjectives agree with the thing possessed, not with the owner.

So if Paul is male, you still say:

• sa sœur = his sister

because sœur is feminine.

Compare:

• son frère = his brother / her brother
• sa sœur = his sister / her sister
• ses parents = his/her parents

So sa does not tell you whether the owner is male or female. It only matches sœur.

By itself, sa sœur could mean either his sister or her sister.

French possessive adjectives:

• son
• sa
• ses

do not show the gender of the owner. They show the gender and number of the noun that follows.

In this sentence, because the subject is Paul, we naturally understand sa sœur as his sister.

So:

• Paul ... sa sœur = Paul ... his sister

Yes. Examine in French is very close to the English verb to examine.

Here:

• sa sœur examine la fissure = his sister examines the crack

It means she is looking at it carefully or inspecting it.

Because the words are related, this is a useful cognate. Just remember that the pronunciation is French, and the conjugation follows French grammar:

• j’examine
• tu examines
• il/elle examine

French often uses an article where English sometimes might not emphasize one as strongly.

Here, la fissure means the crack. It refers to a specific crack in the wall that they are looking at.

In French, singular countable nouns very commonly need a determiner such as:

• le / la / l’ = the
• un / une = a/an
• a possessive like mon, sa, leur

So examine fissure would be ungrammatical. You need something like:

• examine la fissure
• examine une fissure

Because dans le mur suggests the crack is in the wall, not just on its surface.

A fissure is typically thought of as something that forms inside or through the wall structure, so French naturally says:

• la fissure dans le mur = the crack in the wall

If you said sur le mur, that would sound more like something located on the surface of the wall, such as:

• a poster
• a stain
• a picture

So dans is the natural choice for a crack.

Yes. The sentence is in the present tense:

• tient
• examine

In French, the simple present can often mean either:

• a general present: Paul holds
• or an action happening now: Paul is holding

So in context, this sentence most naturally means:

• Paul is holding the ladder while his sister is examining the crack in the wall.

French often uses the simple present where English might prefer is holding or is examining.

French word order is usually straightforward here:

• pendant que = while
• sa sœur = subject
• examine = verb
• la fissure = object
• dans le mur = prepositional phrase

So the clause follows the normal pattern:

subject + verb + object

That gives:

• sa sœur examine la fissure dans le mur

This is one reason the sentence is good for learners: even though it has a subordinate clause, the internal word order is still very regular.

Here are some helpful pronunciation notes:

• Paul ≈ Pol
• tient ≈ sounds like tyan with a nasal vowel; the final t is silent
• l’échelle ≈ lay-shell
• pendant que ≈ pahn-dahn kuh
• sa sœur ≈ sa suhr
  The vowel in sœur does not exist exactly like that in English, but suhr is a rough guide.
• examine ≈ eg-zah-meen
• la fissure ≈ la fee-syur
• dans le mur ≈ dahn luh muur, with dans nasalized

A few extra points:

• sœur has the ligature œ, which is common in some French words.
• In l’échelle, the apostrophe shows elision: la échelle becomes l’échelle.
• French r in sœur, fissure, and mur is pronounced in the back of the throat.

Sometimes, yes, but the nuance is a little different.

• pendant que mainly means while, focusing on two actions happening at the same time.
• alors que can also mean while, but it often suggests more of a contrast.

In this sentence, pendant que is the most natural choice because the main idea is simultaneous action:

• Paul holds the ladder
• his sister examines the crack

If you used alors que, it might sound like you want to contrast the two actions more than simply describe them.

The sentence has two main parts:

1. Paul tient l’échelle
   = main clause

2. pendant que sa sœur examine la fissure dans le mur
   = subordinate clause introduced by pendant que

So the pattern is:

main clause + while-clause

Breaking it down:

• Paul = subject
• tient = verb
• l’échelle = object
• pendant que = conjunction introducing a time relationship
• sa sœur = subject of the second clause
• examine = verb
• la fissure = object
• dans le mur = prepositional phrase describing where the crack is

This is a very useful French sentence pattern for describing two simultaneous actions.