En décembre, mon beau-père achète un sapin, et ma belle-mère accroche une guirlande rouge dans le salon.

French normally uses en with months, seasons, and years:

• en décembre = in December
• en été = in summer
• en 2026 = in 2026

So en décembre is the standard way to say in December.

They are fixed compound family terms in French, and these are traditionally written with a hyphen:

• un beau-père
• une belle-mère

The hyphen is part of the normal spelling. You will see the same with plurals:

• des beaux-pères
• des belles-mères

Not really. In these family expressions, beau and belle are part of an idiomatic meaning.

So:

• beau-père = father-in-law or stepfather
• belle-mère = mother-in-law or stepmother

It does not mean beautiful father or beautiful mother.

Usually, only context tells you.

French uses the same words for both relationships:

• beau-père = father-in-law / stepfather
• belle-mère = mother-in-law / stepmother

If someone wants to be very clear, they may add extra information, but in everyday French the basic terms are often enough.

Because French possessive adjectives agree with the noun possessed, not with the owner.

• beau-père is masculine, so: mon beau-père
• belle-mère is feminine, so: ma belle-mère

This has nothing to do with whether the speaker is male or female.

Because acheter is a stem-changing verb in the present tense.

The e in the stem often changes to è in forms where the ending is silent:

• j’achète
• tu achètes
• il / elle achète
• ils / elles achètent

But:

• nous achetons
• vous achetez

So mon beau-père achète is the correct present-tense form.

French often uses the present tense for:

• habits
• repeated actions
• general descriptions
• typical seasonal routines

So this sentence can describe what usually happens in December, not only what is happening right now.

In French, a singular countable noun usually needs a determiner such as un, une, le, la, etc.

So:

• un sapin = a fir tree / a Christmas tree

You normally cannot just say achète sapin.

Also, in a December/holiday context, un sapin is often understood as a Christmas tree, even without saying de Noël.

In French, most color adjectives come after the noun.

So:

• une guirlande rouge
• une voiture bleue
• un pull vert

That is why French says guirlande rouge, not usually rouge guirlande.

Because rouge already has the same form in the masculine and feminine singular.

So you get:

• un pull rouge
• une guirlande rouge

Only the plural changes in writing:

• des pulls rouges
• des guirlandes rouges

So the adjective does agree, but in the singular you just do not see a spelling change.

There are two useful points here:

1. dans
   French uses dans to mean in / inside a room or enclosed space.
   So dans le salon = in the living room.

2. le salon
   French often uses the definite article for rooms and familiar parts of a house:

   • dans le salon
   • dans la cuisine
   • dans la chambre

So dans le salon is the natural choice here.

Not always. In French, a comma before et is often optional.

So both of these can be acceptable:

• En décembre, mon beau-père achète un sapin et ma belle-mère accroche une guirlande rouge dans le salon.
• En décembre, mon beau-père achète un sapin, et ma belle-mère accroche une guirlande rouge dans le salon.

The comma can make the sentence feel a little more separated or balanced, but it is not required.

A few useful pronunciation notes:

• décembre → final e is silent
• beau-père → beau sounds like bo
• achète → the è is an open eh sound
• sapin → the -in is a nasal vowel
• guirlande → the gui- sounds like gee
• rouge → ends with the zh sound, like the s in measure
• salon → the -on is nasal

A rough pronunciation guide for some words:

• beau-père ≈ bo-pehr
• achète ≈ ah-shet
• sapin ≈ sa-pan with a nasal ending
• rouge ≈ roozh
• salon ≈ sa-lon with a nasal ending

Also, et is pronounced ay, and the final t is silent.