У новых сандалий мягкий ремешок, поэтому в них удобно ходить по городу.

Russian often expresses possession with у + genitive rather than with a verb like to have.

So:

У новых сандалий мягкий ремешок

literally looks more like:

At the new sandals, there is a soft strap

but the natural English meaning is:

The new sandals have a soft strap

Using иметь for ordinary possession is possible, but it often sounds more formal or less natural here. For everyday descriptions of what someone or something has, у + genitive is very common.

Because у requires the genitive case.

The base form is:

• новые сандалии = new sandals

After у, it becomes:

• у новых сандалий

The adjective has to agree with the noun, so both change together:

• новые → новых
• сандалии → сандалий

So this is simply normal case agreement after у.

Usually it means one pair.

In Russian, items that come in pairs are often referred to in the plural even when talking about a single pair:

• ботинки = shoes/boots
• сапоги = boots
• сандалии = sandals

So у новых сандалий most naturally means the new pair of sandals has..., not necessarily several pairs.

In the present tense, Russian often leaves out есть in possession sentences.

So:

• У новых сандалий мягкий ремешок = normal, neutral
• У новых сандалий есть мягкий ремешок = possible, but more emphatic or contrastive

The version without есть is the most natural here.

Here the singular is being used to describe a general feature of the sandals, not to count every individual strap.

Russian often does this when talking about design or material details. So мягкий ремешок can mean something like:

• the strap is soft
• the sandals have soft strapping
• the strap part is soft

If the speaker wanted to emphasize multiple straps, they could say мягкие ремешки, but the singular sounds perfectly natural in a general description.

Yes, formally ремешок is a diminutive-type form related to ремень. But in practice, for clothing and accessories, ремешок often just means strap or small band and sounds completely normal.

So here it does not necessarily sound cute or emotional. It simply fits the object well, because sandal straps are small and narrow.

There are two things going on here.

First, with clothing and footwear, Russian commonly uses в to mean in / wearing:

• в этих ботинках
• в новых сандалиях
• в них

So в них удобно ходить means it’s comfortable to walk in them.

Second, after a preposition, third-person pronouns usually get an initial н-:

• их → в них
• его → у него
• её → с ней

So в них is the correct form after the preposition в.

Here удобно is part of an impersonal construction.

Russian often uses words like:

• удобно = comfortable / convenient
• трудно = difficult
• интересно = interesting
• легко = easy

followed by an infinitive:

• удобно ходить
• трудно понять
• интересно читать

So в них удобно ходить literally means something like:

In them, [it is] comfortable to walk

Russian does not need a dummy subject like English it.

Because ходить is used for general, repeated, habitual, or non-directional walking, while идти is used for one specific trip or movement in progress.

This sentence is not about one single walk. It is saying that these sandals are suitable for walking around the city in general. That makes ходить the right choice.

Compare:

• В них удобно ходить по городу = They’re comfortable for walking around the city
• В них удобно идти домой = They’re comfortable to wear while walking home

After по in this meaning, Russian uses the dative case.

So:

• город → городу

Ходить по городу means to walk around the city or through the city.

This use of по emphasizes movement within an area. It is very common with places:

• гулять по парку = walk around the park
• ходить по магазину = walk around the store
• ездить по стране = travel around the country

So по городу is more specific than just в городе, which only means in the city in a general location sense.

Поэтому means therefore, so, or that’s why.

It introduces the result of the first clause:

• У новых сандалий мягкий ремешок = the new sandals have a soft strap
• поэтому в них удобно ходить по городу = so they’re comfortable to walk around the city in

The comma is there because Russian separates these linked clauses in writing. The structure is:

cause, therefore result

So the punctuation is standard and natural here.