Learn Hardcore German: Jedes Etagenbett im Schlafsaal hat eine kleine Lampe und eine Steckdose. - Every bunk bed in the dormitory has a small lamp and a socket.

jedes is the nominative singular neuter form of jeder (every/each).
The subject of the sentence is Jedes Etagenbett, so it must be in the nominative case.

Forms of jeder in the nominative:

masculine: jeder Mann
feminine: jede Frau
neuter: jedes Bett

So jedes Etagenbett is correct because:

neuter noun (das Etagenbett)
subject (nominative)
so: jedes.

What exactly does Etagenbett mean, and how is it different from other “bed” words?

Etagenbett literally means something like “storey bed” or “tiered bed”, and it’s the normal word for a bunk bed.

Common related words:

das Etagenbett – bunk bed
das Hochbett – a loft bed (raised bed with space underneath, not necessarily two beds)
das Doppelbett – double bed
das Einzelbett – single bed

So in a dormitory (Schlafsaal), Etagenbett is the standard word you’d expect.

What does im Schlafsaal mean exactly, and why im and not in dem?

im is just a contraction of in dem:

in can take the dative when it means “in/inside (location)”.
Schlafsaal is masculine: der Schlafsaal.
Dative singular of der Schlafsaal is dem Schlafsaal.

So:

in dem Schlafsaal → im Schlafsaal (this contraction is standard and very common).

The meaning is “in the dormitory” (location, not movement), which is why the dative is used.

Why is the verb hat and not haben in this sentence?

The verb agrees with the subject, which is Jedes Etagenbett.

Jedes Etagenbett is grammatically singular (“each bunk bed”).
For er/sie/es (3rd person singular), the form of haben is hat.

So even though you’re talking about many beds overall, the grammar focuses on each one individually, so you use the singular:

Jedes Etagenbett … hat … = Each bunk bed … has …
If you talked about all beds together:
Alle Etagenbetten … haben … = All the bunk beds … have …

Which case are eine kleine Lampe and eine Steckdose in, and why?

Both eine kleine Lampe and eine Steckdose are in the accusative case as direct objects of hat.

Structure of the sentence:

Subject (nominative): Jedes Etagenbett im Schlafsaal
Verb: hat
Direct objects (accusative): eine kleine Lampe und eine Steckdose

Each bed has what? → a lamp and a socket.
So both noun phrases are accusative.

Why is it eine kleine Lampe but just eine Steckdose (no adjective)? What’s going on with kleine?

Lampe and Steckdose are both feminine nouns:

die Lampe
die Steckdose

When you have a feminine noun in the accusative with eine and an adjective, the adjective ending is -e:

eine kleine Lampe (accusative, feminine, with adjective)

If there’s no adjective, you just have:

eine Steckdose (accusative, feminine, no adjective → no adjective ending needed)

So nothing special is happening with Steckdose—it simply has no adjective.
If you added one, you’d say:

eine praktische Steckdose
eine einzelne Steckdose

The pattern would be the same: eine + adjective with -e + feminine noun in the accusative.

Could I change the word order, like Im Schlafsaal hat jedes Etagenbett eine kleine Lampe und eine Steckdose?

Yes, that word order is perfectly correct and natural.

German allows some flexibility with word order as long as:

the finite verb (here: hat) stays in second position, and
the meaning remains clear.

Some possible versions:

Jedes Etagenbett im Schlafsaal hat eine kleine Lampe und eine Steckdose.
Im Schlafsaal hat jedes Etagenbett eine kleine Lampe und eine Steckdose.

Both mean the same thing; the second version just emphasizes im Schlafsaal a bit more.

What’s the difference between Steckdose, Stecker, and similar words?

These words are easy to mix up:

die Steckdose – the power outlet / wall socket
der Stecker – the plug (the thing on the cable that you put into the socket)
die Steckleiste or Mehrfachsteckdose – a power strip (multiple outlets in one strip)

In this sentence, Steckdose is correct because each bed has its own outlet.

How would I say this sentence in the plural, like “All the bunk beds in the dorm have …”?

You would change the subject to plural and adjust the verb and noun endings:

Alle Etagenbetten im Schlafsaal haben kleine Lampen und Steckdosen.

Changes:

Jedes Etagenbett → Alle Etagenbetten (plural)
hat → haben (3rd person plural)
The objects become plural to match the idea: each bed has its own lamp and socket → together: Lampen and Steckdosen.

You could also keep the objects conceptually singular per bed, but usually people pluralize them as above.

Could I say in einem Schlafsaal instead of im Schlafsaal? What would be the difference?

Yes, you can say:

Jedes Etagenbett in einem Schlafsaal hat eine kleine Lampe und eine Steckdose.

Difference:

im Schlafsaal (in dem Schlafsaal) = in the dormitory (specific, known dorm)
in einem Schlafsaal = in a dormitory (non-specific, any dorm of that type)

Grammatically, einem Schlafsaal is dative singular masculine (after in for location), just like dem Schlafsaal—only the article (definite vs. indefinite) is different.