Learn Hardcore Swedish: Han lägger locket på kastrullen.

lägga – to put something so that it lies (usually flat or “lying” position)
ställa – to put something so that it stands (upright, on its base)
sätta – to set or seat something/someone (often for people, or abstractly)

A lock (lid) is placed so that it lies on the pot, not stands up, so Swedes say:

lägga locket på kastrullen – put/lay the lid on the saucepan

Using sätta or ställa here would sound wrong in standard Swedish.

Why is it locket and not just lock?

Locket is the definite form of lock (lid), meaning “the lid”.

indefinite: ett lock – a lid
definite: locket – the lid

In Swedish, the definite article (the) is usually added as a suffix to the noun, not as a separate word. So instead of the lid, you get locket.

The sentence talks about a specific lid, so the definite form is used.

Why is it kastrullen and not kastrull?

Same idea as with locket: kastrullen is the definite form of kastrull (saucepan, pot), meaning “the saucepan”.

indefinite: en kastrull – a saucepan
definite: kastrullen – the saucepan

So på kastrullen means “on the saucepan”, not just on a saucepan.

Why does Swedish attach “the” to the end of the nouns (locket, kastrullen) instead of using a separate word like English?

Swedish usually marks definiteness with endings (suffixes) rather than a separate word:

ett lock → locket (a lid → the lid)
en kastrull → kastrullen (a saucepan → the saucepan)

There is no separate word like the in front of the noun in basic cases.
This is just a core feature of Swedish grammar: definite noun = noun + ending.

Why is the preposition på used here, and does it mean “on” or “onto”?

På literally means on, but with verbs of movement like lägga, the combination lägga X på Y often corresponds to English put X on (onto) Y.

In this sentence:

lägger locket på kastrullen = puts/is putting the lid on (onto) the saucepan

Swedish doesn’t need a separate preposition to show motion (onto vs on). På covers both the idea of on and onto here; the movement is already clear from lägger.

Could you change the word order, for example say Han lägger på locket på kastrullen?

The normal, most natural word order is:

Han lägger locket på kastrullen.

You can also say:

Han lägger på locket. – He puts the lid on.

Here lägger på locket works as a unit: lägga på + object, meaning put on (the lid), and the thing you put it on is either known from context or omitted as unimportant.

But Han lägger på locket på kastrullen is clumsy and sounds off; Swedes would almost always avoid that and just say:

Han lägger locket på kastrullen.

Is på kastrullen part of a phrasal verb like English “put on”, or is på just a normal preposition?

Here, på is best understood as a normal preposition meaning on:

locket = the direct object (what is being moved)
på kastrullen = prepositional phrase (where it is put)

However, Swedish also has the verb + particle combination lägga på, which can mean things like add or put on (more), for example:

Lägg på mer pasta. – Add more pasta.

So:

in lägger locket på kastrullen, på behaves like a spatial preposition: on the saucepan.
in lägga på mer, på is more like a particle (part of the verb meaning).

Why is it ett lock but en kastrull? How do I know which gender to use?

Swedish has two grammatical genders:

en-words (common gender): e.g. en kastrull
ett-words (neuter): e.g. ett lock

Their definite forms are:

en kastrull → kastrullen
ett lock → locket

Unfortunately, there is no simple rule that tells you the gender of every noun. You generally have to:

learn the noun together with its article (e.g. en kastrull, ett lock)
memorize patterns over time (many but not all words with certain endings are en, etc.)

In this sentence, you just have to know that:

lock is ett
kastrull is en

Does Han always mean a male person, and could you use hon or hen here instead?

han = he (male person)
hon = she (female person)
hen = gender‑neutral singular pronoun, often used when gender is unknown, irrelevant, or non-binary

In this specific sentence, Han lägger locket på kastrullen clearly refers to a man or boy.
If you wanted a woman, you’d say:

Hon lägger locket på kastrullen.

If you wanted to avoid specifying gender:

Hen lägger locket på kastrullen.

How do you pronounce lägger, locket, and kastrullen?

Approximate pronunciations (Swedish varies by region, this is a common standard-like version):

lägger: roughly [ˈlɛɡːɛr]
- läg- like “leg” with a slightly more open e
- -ger like “ger” in “gender” but with a clear e sound
locket: roughly [ˈlɔkːɛt]
- lo- like “lock” in English but shorter
- doubled k makes the k sound short and strong
kastrullen: roughly [kasˈtrɵlːɛn]
- kas- like “cuss”
- -trull-: u is like the vowel in French “feu” or German “schön”; double l = long l
- final -en with a short, unstressed e
  - n

Could you leave out kastrullen and just say Han lägger på locket? Does it still sound complete?

Yes:

Han lägger på locket.

is a perfectly natural and complete sentence. It means He puts the lid on, and it’s understood that there is some pot, pan, or container involved, even if you don’t say which one.

Adding på kastrullen simply specifies where he is putting the lid:

Han lägger på locket på kastrullen. – technically understandable but not idiomatic.
Han lägger locket på kastrullen. – idiomatic and natural.