На пляже стоял длинный ряд шезлонгов, и мы выбрали два места у воды.

Russian uses на with пляж to mean on the beach / at the beach.

• на пляже = on/at the beach
• в is usually used for being inside something

So a beach is understood as an open surface/location, not an enclosed space, which is why на is the normal choice.

Also, пляже is in the prepositional case because it follows на in a location meaning:

• пляж → на пляже

Because the grammatical subject is not шезлонгов but ряд.

The phrase is:

• длинный ряд шезлонгов = a long row of deck chairs

The main noun is ряд (row), and ряд is masculine singular, so the verb agrees with it:

• ряд стоял = the row stood / was positioned

Even though the row contains many deck chairs, the verb still matches ряд, not шезлонгов.

Because ряд is a masculine noun.

So the adjective must also be masculine nominative singular:

• длинный ряд = a long row

Compare:

• длинная for feminine nouns
• длинное for neuter nouns
• длинный for masculine nouns

Because after ряд Russian normally uses the genitive plural:

• ряд шезлонгов = a row of deck chairs

This is similar to English of deck chairs. Russian often expresses that relationship by putting the second noun into the genitive.

So:

• dictionary form: шезлонг
• genitive plural: шезлонгов

Yes, literally стоял means stood, but in Russian verbs like стоять, лежать, and висеть are often used where English simply uses was / were.

So:

• На пляже стоял длинный ряд шезлонгов
  literally: On the beach stood a long row of deck chairs
• natural English: There was a long row of deck chairs on the beach

Russian likes to describe how something is positioned:

• стоять = stand
• лежать = lie
• висеть = hang

Выбрали is perfective past tense, which means the action is seen as completed.

Here the idea is:

• we made the choice
• the choice was finished

So мы выбрали два места means:

• we chose two spots/seats

If you used выбирали instead, it would suggest an ongoing or repeated process:

• we were choosing
• we spent time choosing

In this sentence, the result matters, so выбрали is the natural choice.

There are two things happening here.

1. Why два, not две?

Because место is a neuter noun.

• два is used with masculine and neuter nouns
• две is used with feminine nouns

So:

• два места = correct
• две места = incorrect

2. Why места?

After the numbers 2, 3, 4, Russian usually uses the noun in a special form that looks like the genitive singular:

• одно место
• два места
• три места
• четыре места

So два места is exactly what you expect.

It can mean either, depending on context.

The basic meaning of место is place / spot / seat. In this sentence, since we are talking about deck chairs on a beach, два места у воды most naturally means:

• two spots near the water
• possibly two seats/sunbeds near the water

Russian often uses место in a broader way than English seat.

У usually means by, near, next to, and it requires the genitive case.

So:

• вода → воды
• у воды = by the water / near the water

On a beach, this means near the shoreline, not literally inside the water.

Because they are in different cases after different prepositions.

на пляже

• на with location takes the prepositional case
• пляж → пляже

у воды

• у takes the genitive case
• вода → воды

So the noun changes depending on the preposition and the grammatical role.

Yes, был is possible in some contexts, but стоял is more vivid and natural here.

Compare:

• На пляже был длинный ряд шезлонгов
  = There was a long row of deck chairs on the beach
• На пляже стоял длинный ряд шезлонгов
  = A long row of deck chairs stood on the beach

The second version gives a stronger visual sense of arrangement and physical presence. Russian often prefers these position verbs where English would simply say was.

Because и is joining two separate clauses, each with its own subject/action:

1. На пляже стоял длинный ряд шезлонгов
2. мы выбрали два места у воды

In Russian, when и connects two full clauses, a comma is often used.

So the comma helps show that these are two linked statements:

• first, what was there on the beach
• second, what we did

The word order is natural, but Russian word order is more flexible than English.

This sentence starts with the setting:

• На пляже = On the beach

Then it introduces what was there:

• стоял длинный ряд шезлонгов

Then it adds the next action:

• и мы выбрали два места у воды

A different order is sometimes possible, but this version sounds smooth and descriptive. Russian often puts location first when setting the scene.