Learn Hardcore Russian: Маленький стол стоит у окна. - The small table is standing by the window.

Маленький – adjective, masculine, singular, nominative (agrees with стол).
стол – noun, masculine, inanimate, singular, nominative (subject of the sentence).
стоит – verb, 3rd person singular, present tense, imperfective, from стоять (to stand).
у – preposition that takes the genitive case, here meaning by / near.
окна – noun, neuter, singular, genitive (after у), dictionary form is окно (window).

Why is it маленький стол and not маленькая стол or маленькое стол?

In Russian, adjectives must agree with the noun in gender, number, and case.

стол is masculine, singular, nominative.
The basic masculine nominative ending for this type of adjective is -ый / -ий.
So the correct form is маленький стол.

If the noun were feminine, like лампа (lamp), you would say маленькая лампа.
If it were neuter, like окно, you would say маленькое окно.

Why do we use стоит here? In English we usually say is, not stands.

Russian often uses verbs of position instead of a general to be when describing where something is:

стоять – to stand (upright position)
лежать – to lie (horizontal)
сидеть – to sit

A table is normally thought of as standing on its legs, so стоит is very natural:
Маленький стол стоит у окна = The small table is (stands) by the window.

You could technically omit the verb in some contexts (Маленький стол у окна), but стоит sounds more complete and neutral in standard speech and writing.

What is the infinitive of стоит, and what exactly does стоять mean?

The infinitive is стоять.
Basic meaning: to stand (be in an upright, vertical position).

In practice, стоять can also mean simply to be located in a standing position. For objects like tables, chairs, cupboards, buildings, etc., стоять is the usual verb when you talk about where they are.

So стоит in this sentence is the 3rd person singular present form of стоять referring to стол.

Could we say Маленький стол у окна without стоит? Is that correct?

Yes, Маленький стол у окна is grammatically correct and understandable.

Nuance:

Маленький стол стоит у окна – a normal, full sentence; explicitly describes the table as standing there.
Маленький стол у окна – shorter, a bit more like a label or a note, or something you might say in quick, informal speech.

Both are possible, but if you want a neutral, complete sentence in most contexts, стоит is the better choice.

Why is it у окна and not у окно? What case is окна?

The preposition у (meaning by / near / at) requires the genitive case.

Dictionary form: окно (nominative singular).
Genitive singular: окна.

So:

у окна literally means by (of) the window, but it is translated as near the window / by the window.

That is why окна is used, not окно.

Can I replace у окна with something like возле окна or рядом с окном? Are they different?

Yes, you can, and they are close in meaning:

у окна – by the window, at the window, near the window (very common, short, neutral).
возле окна – near the window, slightly more explicit about being close.
рядом с окном – next to the window, beside the window.

All of these are fine; the differences are subtle. In most everyday contexts they are interchangeable, though у окна is the most compact and very idiomatic.

Why is окна singular and not plural, like у окон?

Окна here is genitive singular, not plural.

Genitive singular of окно is окна.
Genitive plural of окно is окон.

So:

у окна – by the window (one window).
у окон – by the windows (several windows).

In the sentence Маленький стол стоит у окна, we are talking about one window, so окна (genitive singular) is correct.

Can the word order change? Is У окна стоит маленький стол also correct?

Yes, Russian word order is flexible, and both are correct:

Маленький стол стоит у окна.
More neutral, subject-first order. Slightly emphasizes the small table as the topic.
У окна стоит маленький стол.
Brings у окна to the front, so the place (by the window) is highlighted.
It feels more like: By the window, there is a small table.

The basic meaning is the same, but the focus changes slightly depending on what you put first.

Can I say столик instead of стол? What is the difference?

Yes, you can say:

Маленький столик стоит у окна.

Столик is a diminutive of стол. It usually suggests:

a smaller, lighter, or more informal table (coffee table, bedside table, little side table),
or a nuance of something small and maybe a bit more cozy or cute.

So:

маленький стол – a small table (neutral).
маленький столик – a small little table / small side table (often sounds more natural in a home context).

Why is there no separate word for a or the before стол in Russian?

Russian has no articles like English a / an / the.

The phrase маленький стол can mean:

a small table, or
the small table,

depending on context.
You understand whether it is a or the from the situation or previous sentences, not from a special word. The original Russian sentence itself does not force one or the other.

How do you pronounce the sentence, and where are the stresses?

Stresses:

мАленький – stress on ма.
стол – one syllable, so it is fully stressed.
стои́т – stress on ит (sto-ít).
у – short u sound, unstressed.
окнА – stress on на (ok-ná).

Approximate pronunciation:
mA-lin-kij stol sta-Ít u ok-NÁ (with Russian vowel quality, of course).