Im Sommer trage ich lieber Sandalen als geschlossene Schuhe.

Im is a contraction of in dem.

In this sentence, in is being used in a time expression: im Sommer = in the summer / during summer. German very often uses in + dative for seasons, months, and similar time phrases:

• im Sommer
• im Winter
• im Januar

So im Sommer is the normal idiomatic form.

German main clauses usually put the finite verb in second position.

Here, Im Sommer comes first, so the verb trage must come next:

• Im Sommer trage ich ...

The subject ich comes after the verb because the first position is already taken by Im Sommer.

You could also say:

• Ich trage im Sommer lieber Sandalen als geschlossene Schuhe.

That is also correct. It just starts with ich instead of the time phrase.

Yes, tragen can mean to carry, but it also commonly means to wear when talking about clothes, shoes, glasses, etc.

So in clothing contexts:

• Ich trage eine Jacke. = I’m wearing a jacket.
• Sie trägt Sandalen. = She’s wearing sandals.

This is completely normal German usage.

Here lieber means preferably or rather.

It is the comparative form of gern:

• gern = gladly / like doing
• lieber = rather / prefer
• am liebsten = most of all

So:

• Ich trage lieber Sandalen ... = I prefer to wear sandals ...

German often uses lieber where English uses prefer.

Lieber usually goes close to the thing being preferred.

In this sentence, it modifies the preference for wearing sandals rather than closed shoes, so it appears before Sandalen:

• Ich trage lieber Sandalen ...

That placement sounds natural and standard.

You may also hear slightly different word orders in longer sentences, but this position is the most straightforward one.

German uses als after a comparative idea, and lieber is already comparative.

So:

• lieber ... als ... = rather ... than ...

That is why the sentence says:

• lieber Sandalen als geschlossene Schuhe

Compare:

• größer als = bigger than
• lieber Tee als Kaffee = tea rather than coffee

So als is the correct word here.

German often leaves out articles when speaking generally about plural nouns, especially in statements about habits or preferences.

So:

• Ich trage Sandalen.
• Ich mag geschlossene Schuhe nicht.

This is similar to English:

• I wear sandals
• I don’t like closed shoes

If you added articles, it would sound more specific:

• die Sandalen = the sandals
• die geschlossenen Schuhe = the closed shoes

But here the speaker means sandals and closed shoes in general.

Because geschlossene is an adjective before a plural noun with no article.

German adjective endings depend on:

• gender
• case
• number
• whether there is an article

Here:

• Schuhe is plural
• it is in the accusative case
• there is no article

So the adjective takes the strong ending -e:

• geschlossene Schuhe

Other similar examples:

• rote Äpfel
• warme Tage
• bequeme Sandalen

They are in the accusative case because they are the direct objects of trage.

The speaker is wearing what?

• Sandalen
• geschlossene Schuhe

So both parts of the comparison are accusative.

In the plural, the noun form itself often does not change between nominative and accusative, so you mostly notice the case from sentence function and adjective endings.

Yes, absolutely.

Both are correct:

• Im Sommer trage ich lieber Sandalen als geschlossene Schuhe.
• Ich trage im Sommer lieber Sandalen als geschlossene Schuhe.

The difference is emphasis:

• Im Sommer ... puts focus on when
• Ich ... starts more neutrally with the subject

German is flexible about what comes first, but the finite verb still stays in second position.

Literally, it says than closed shoes, but the full meaning is understood as:

• I prefer wearing sandals rather than wearing closed shoes

German often leaves out repeated material when it is obvious from context. So after lieber, the second half of the comparison can be shortened.

A fuller version would be something like:

• Im Sommer trage ich lieber Sandalen, als geschlossene Schuhe zu tragen.

But that sounds heavier and less natural in everyday speech. The shorter version is much more common.

Yes, it is a normal and natural expression.

Geschlossene Schuhe means shoes that cover the foot more fully, unlike sandals or open-toed shoes.

Depending on context, German speakers might also say more specific things such as:

• feste Schuhe = sturdy shoes
• Halbschuhe = low shoes / regular shoes
• Sneaker = sneakers

But in this sentence, geschlossene Schuhe is a very natural opposite to Sandalen.