Хотя майка и шорты простые, в такую жару они подходят лучше, чем шёлковая блузка.

In Russian, the present-tense form of to be is usually omitted.

So:

• майка и шорты простые literally looks like tank top and shorts simple
• but it means the tank top and shorts are simple/plain

This is completely normal in Russian. If you wanted the past or future, then a form of быть would appear.

No. Here и simply means and and connects майка and шорты.

So the structure is:

• Хотя = although
• майка и шорты = the tank top and the shorts
• простые = are simple/plain

A learner might expect хотя и as a set phrase meaning something like although ... indeed/still, but that is not what is happening here.

Because it describes майка и шорты together.

Even though:

• майка is singular feminine
• шорты is plural

the combined subject майка и шорты is plural overall, so the adjective must also be plural:

• простые = plural

This is the same idea as English the shirt and shorts are simple, not is simple.

Шорты is normally a plural-only noun, like some clothing words in English such as shorts or pants.

So Russian usually says:

• эти шорты = these shorts
• новые шорты = new shorts

A singular form is not normally used in everyday standard Russian.

This is a common Russian expression meaning in such heat or in weather this hot.

Here в + accusative expresses the situation or conditions someone is in:

• в такую жару = in such heat
• в холод = in the cold
• в такую погоду = in such weather

So жару is accusative singular, and такую agrees with it:

• жара = nominative
• жару = accusative

It is not about physical movement into something here; it is an idiomatic way to describe conditions.

Here подходят does not mean physical approaching. It means are suitable, work better, or are a better choice.

The verb подходить can mean:

• to approach
• to suit
• to fit
• to be appropriate

In this sentence, the meaning is about suitability for hot weather:

• они подходят лучше = they suit the situation better / they are more suitable

Because its subject is они, and они refers back to майка и шорты.

So:

• они подходят = they suit / they are suitable

If the subject were singular, the verb would also be singular:

• блузка подходит = the blouse is suitable

Они refers back to майка и шорты and makes the main clause clear and smooth.

Russian can often omit subject pronouns, but here keeping они is very natural because:

• the subject was mentioned in the subordinate clause
• the main clause starts a new statement about that subject
• the comparison becomes clearer

Without они, the sentence would feel less clear and less balanced. So они is helpful, even if Russian often drops pronouns in other contexts.

Because шёлковая блузка is the second item in a comparison, not a direct object.

With лучше, чем..., Russian often uses the nominative after чем, because there is an implied repeated verb:

• они подходят лучше, чем шёлковая блузка [подходит]

So the full sense is:

• they suit this heat better than a silk blouse does

That is why шёлковая блузка stays in the nominative.

Because the sentence is comparing two different clothing options:

• option 1: майка и шорты
• option 2: шёлковая блузка

The first option happens to contain two items, so it is grammatically plural. The second option is one item, so it is singular. Russian does not need both sides of the comparison to match in number.

Because Хотя introduces a subordinate clause:

• Хотя майка и шорты простые = Although the tank top and shorts are simple
• в такую жару они подходят лучше, чем шёлковая блузка = in such heat they are more suitable than a silk blouse

Russian separates this subordinate concessive clause from the main clause with a comma.

Хотя introduces a contrast: although / even though.

The idea is:

• yes, the tank top and shorts are plain/simple
• but despite that, they are still the better choice in this heat

So the sentence has a concessive meaning: one fact might make you expect the opposite, but the main clause overturns that expectation.