Learn Hardcore Russian: В темноте я нашёл выключатель в прихожей и включил свет. - In the dark I found the light switch in the entryway and turned on the light.

Dictionary form: темнота (darkness)
Prepositional singular: (в) темноте
So it’s literally in (the state of) darkness, not “in a dark (room)”—it describes the conditions.

Why is it нашёл and not находил?

Нашёл is perfective past, meaning a completed, successful result: I found (and now I had it / located it).
Находил (imperfective) would usually mean something like used to find, was finding, or focus on the process without emphasizing the result—less natural for “I found the switch (at last)”.

What’s going on with the spelling нашёл vs нашел?

Both refer to the same word, but:

нашёл (with ё) is the accurate spelling and shows the stress: na-SHOL
нашел (with е) is a very common informal/typographic replacement when ё isn’t used
In learning materials, ё is often kept to help pronunciation.

Why is it выключатель if the action is включил свет (“turned on the light”)? Isn’t that contradictory?

Not contradictory: выключатель is the common word for a (light) switch in general, regardless of whether you’re turning something on or off. It comes historically from the idea of “switching off,” but in modern usage it just means the device on the wall.

Why is выключатель in this form? What case is it?

Выключатель is the direct object of нашёл (found what?), so it’s accusative. For many masculine inanimate nouns, nominative = accusative, so the form doesn’t change:

nominative: выключатель
accusative: выключатель

What case is в прихожей, and why does it end in -ей?

В прихожей is also в + prepositional (location): in the hallway/entryway.

Dictionary form: прихожая (feminine, “entryway / hall”)
Prepositional singular: (в) прихожей
Many feminine nouns ending in -ая change to -ой / -ей in the prepositional; here it’s -ей.

What exactly is прихожая? Is it “hallway” or “foyer”?

Прихожая is the entryway area of a home/apartment—where you come in, leave shoes/coats, etc. Depending on the home, it can correspond to entry hall, hallway by the door, foyer. It’s more specific than a generic corridor.

Why is the pronoun я included? Could it be omitted?

Yes, it can often be omitted because the verb ending already marks the person:

В темноте нашёл выключатель… is possible in context.
But я is included to emphasize or clarify who did it (especially if there are multiple people in the story), or simply as a neutral stylistic choice.

Why is there no comma before и?

Because и connects two verbs (нашёл and включил) that share the same subject (я) and form a single coordinated predicate:
я нашёл … и включил …
A comma is typically not used in this simple coordination.

Why is it включил свет and not включил света or включил светом?

Because включить takes a direct object in the accusative: to turn on what? → свет.

света would be genitive and would suggest different constructions/meanings (not used here).
светом (instrumental) would mean “with light,” which doesn’t fit the verb включить.

Why is включил also perfective? Could it be включал?

Включил (perfective) matches the idea of a completed sequence of actions: found the switch and turned on the light.
Включал (imperfective) would more likely mean:

repeated action: (he) used to turn on the light, or
process/background: was turning on the light (less “event-like” and less final).

How is word order working here? Could Russian reorder this sentence?

Russian word order is flexible, but the chosen order is neutral and clear:

В темноте sets the scene first (conditions)
я states the actor
then actions in sequence: нашёл … и включил …
You could reorder for emphasis, e.g. Я в темноте нашёл… (emphasizes “I”), or Выключатель я нашёл… (emphasizes “the switch”), but the original is a natural default.