Lia ŝerco ridigis ĉiujn en la kafejo.

Ridigis is built from:

• rid- = laugh
• -ig- = make/cause
• -is = past tense

So ridigis means made laugh or caused to laugh.

A useful comparison:

• Li ridis = He laughed.
• Li ridigis ĉiujn = He made everyone laugh.

This -ig- suffix is very common in Esperanto.

The -n marks the direct object.

In this sentence, lia ŝerco is the thing doing the action, and ĉiujn is the group affected by it.

So:

• Lia ŝerco = the subject
• ridigis = made laugh
• ĉiujn = everyone / all of them, as the object

Without -n, the grammar would be wrong here.

Because ĉiujn is plural.

• ĉiu = each one, every individual one
• ĉiuj = all, everyone, all people

Then the object ending is added:

• ĉiuj
  • -n = ĉiujn

So ĉiujn means everyone or all of them as the direct object.

This is a very common question.

• lia = his
• sia = his/her/their own, referring back to the subject of the clause

In this sentence, the grammatical subject is ŝerco:

• Lia ŝerco ridigis ĉiujn.
• Subject = ŝerco

Because the subject is the joke, not he, you do not use sia here.

So:

• lia ŝerco = his joke
• sia ŝerco would try to mean its own joke, referring back to ŝerco, which does not make sense here

Ŝerco means joke.

It is a regular noun:

• ŝerc-o
  
  • ŝerc- = joke / joking idea
  • -o = noun ending

You may also see related forms such as:

• ŝerci = to joke
• ŝerca = joking, humorous

Kafejo means café or coffeehouse.

It is made from:

• kaf- = coffee
• -ej- = place
• -o = noun

So literally, kafejo is a place for coffee.

The suffix -ej- is very useful in Esperanto. It often means place for or place where something happens.

La is the definite article, meaning the.

So:

• en kafejo = in a café
• en la kafejo = in the café

The sentence uses la because it refers to a specific café, or at least one treated as identifiable in the context.

Unlike English, Esperanto has only one article: la. There is no separate word for a/an.

It most naturally tells you where the event happened: the making-everyone-laugh happened in the café.

So the normal understanding is:

• his joke made everyone laugh
• and this happened in the café

In practice, it also strongly suggests that the people laughing were the people in the café.

Esperanto allows this kind of phrase just like English does, where location can describe the whole event.

The ending -is marks the past tense.

So ridigis means that the action happened in the past:

• ridigas = makes laugh
• ridigis = made laugh
• ridigos = will make laugh

This tense system is very regular in Esperanto.

Yes, Esperanto word order is fairly flexible because endings show the grammar.

This sentence is in a very natural order:

• Lia ŝerco ridigis ĉiujn en la kafejo.

But other orders are possible, for example:

• En la kafejo lia ŝerco ridigis ĉiujn.

That still means essentially the same thing, because ĉiujn keeps the object marker -n.

Even so, the original order is the most straightforward for learners.

No. Esperanto nouns do not have grammatical gender.

So ŝerco is not masculine or feminine. It is just the noun joke.

Lia tells you about the owner:

• lia ŝerco = his joke
• ŝia ŝerco = her joke

The noun itself does not change gender.

Yes. A common alternative would be:

• Lia ŝerco igis ĉiujn ridi.

This literally means His joke made everyone laugh too.

Compare:

• ridigis = made laugh
• igis ... ridi = made ... laugh

Both are good Esperanto. The sentence you were given uses the compact -ig- form, which is very typical and elegant.