Mon oncle cherche une scie parce qu’il doit scier une vieille planche dans le jardin.

Because oncle is a masculine singular noun in French, so the correct possessive adjective is mon.

• mon = my + masculine singular noun
• ma = my + feminine singular noun
• mes = my + plural noun

So:

• mon oncle = my uncle
• ma tante = my aunt
• mes cousins = my cousins

Cherche is the present tense form of chercher used with il / elle / on.

So:

• je cherche = I am looking for / I look for
• tu cherches
• il cherche
• elle cherche
• on cherche

In this sentence, the subject is mon oncle, so French uses the il form:

• Mon oncle cherche...

Also, the French present tense can often mean either:

• looks for
• is looking for

depending on context.

Yes. Scie is a feminine noun, so it takes une:

• une scie = a saw

In French, grammatical gender is part of the noun, and it does not always match anything logical in English. You simply learn the noun together with its article:

• une scie
• une planche

That helps you remember the gender.

Because they are directly related words:

• une scie = a saw
• scier = to saw

This is similar to English pairs like:

• a hammer / to hammer

So in the sentence:

• une scie is the tool
• scier is the action done with that tool

That relationship is very common in French.

Doit comes from the verb devoir, which often means must, have to, or be supposed to.

Here:

• il doit scier = he has to saw / he must saw

This is a very common French pattern:

• conjugated verb + infinitive

Examples:

• il doit partir = he has to leave
• elle veut manger = she wants to eat
• nous pouvons venir = we can come

So doit is the conjugated verb, and scier stays in the infinitive.

Because French normally avoids que directly before a vowel sound. It shortens que to qu’. This is called elision.

So:

• parce que + il becomes parce qu’il

The same thing happens in many other places:

• que elle → qu’elle
• je ai → j’ai
• le ami → l’ami

So parce qu’il is just the normal shortened form before il.

In French, many adjectives come after the noun, but some common ones often come before it. Words about age, size, beauty, and goodness are often placed before the noun.

Vieux / vieille is one of those common adjectives.

So:

• une vieille planche = an old board/plank

Also, planche is feminine, so vieux changes to vieille.

Compare:

• un vieux livre = an old book
• une vieille maison = an old house

Because planche is feminine singular.

The adjective vieux changes to match the noun:

• vieux = masculine singular
• vieille = feminine singular
• vieux = masculine plural
• vieilles = feminine plural

So:

• un vieux jardin
• une vieille planche

This agreement between noun and adjective is a basic French rule.

Planche usually means board or plank, depending on context.

In this sentence, since someone wants a saw and needs to cut it, board or plank both fit well. The important grammar point is that planche is feminine:

• une planche
• une vieille planche

Dans le jardin is the most natural way to say in the garden in a sentence like this.

• dans focuses on being inside / in a place
• au jardin exists in some contexts, but it is less neutral here and can sound more literary, regional, or context-specific

So for a learner, the safest and most standard choice is:

• dans le jardin = in the garden

In natural reading, it most likely goes with the second part of the sentence:

• he needs to saw an old board in the garden

But in real life, the exact attachment can be a little flexible, just as in English. Context usually makes it clear.

French often places location phrases at the end like this, and readers understand them from the situation.

Usually, yes. In most everyday sentences, parce que is the normal way to say because.

Here:

• parce qu’il doit scier... = because he has to saw...

French also has car, which can also mean for / because, but parce que is more common in ordinary speech.

So for this sentence, parce que is exactly what you would expect.

It breaks down like this:

• Mon oncle = subject
• cherche = main verb
• une scie = direct object
• parce qu’ = because
• il doit scier = he has to saw
• une vieille planche = object of scier
• dans le jardin = place expression

So the pattern is:

• [subject] + [verb] + [object] + parce que + [subject] + [modal verb] + [infinitive] + [object] + [place]

That is a very common and useful French sentence pattern.