La policistino diris al la biciklistino: “Ne forgesu vian kaskon kaj rigardu ambaŭflanken antaŭ ol vi transiras.”

La is the definite article, like English the. It shows that the sentence is talking about specific people, not just any policewoman or any cyclist in general.

So:

• la policistino = the policewoman
• la biciklistino = the female cyclist

This is natural when a story or situation already identifies the people involved.

The ending -in- is the Esperanto suffix for female persons.

So:

• policisto = police officer
• policistino = female police officer
• biciklisto = cyclist
• biciklistino = female cyclist

The final -o is the normal noun ending, so these words break down like this:

• policist-in-o
• biciklist-in-o

Al means to and marks the person something is said to.

So:

• La policistino diris al la biciklistino = The policewoman said to the cyclist

This is the normal pattern with diri when you include the listener:

• diri al iu = to say to someone

Without al, the grammar would be wrong here.

Diris is the past tense. The sentence is narrating something that already happened:

• diras = says / is saying
• diris = said

So the structure is:

• first, the narration: La policistino diris...
• then, the actual words she said

The -u ending is the Esperanto volitive form. It is used for commands, requests, instructions, wishes, and similar ideas.

Here it gives commands:

• forgesu = forget! / do forget
• ne forgesu = don’t forget
• rigardu = look

So Ne forgesu vian kaskon kaj rigardu... means the policewoman is instructing the cyclist what to do.

In Esperanto, commands use the -u form, even in negatives.

So:

• forgesi = to forget
• forgesu = forget!
• ne forgesu = don’t forget!

The infinitive forgesi cannot be used by itself as a command.

Because kaskon is the direct object, and adjectives or related words must agree with the noun they describe.

Here:

• kasko = helmet
• kaskon = helmet as a direct object
• via = your
• vian = your, agreeing with an -n noun

So:

• vian kaskon = your helmet

This agreement is very regular in Esperanto. If the noun gets -n, the modifying word gets -n too.

Ambaŭflanken is an adverb meaning to both sides or, in natural English, both ways.

The final -n is the directional -n, which often appears in adverbs showing movement or direction:

• hejme = at home
• hejmen = homeward, to home
• dekstre = on the right
• dekstren = to the right

In rigardu ambaŭflanken, the idea is look to both sides. In English we usually say look both ways.

Antaŭ ol means before when it introduces a whole clause.

So:

• antaŭ ol vi transiras = before you cross

This is different from using antaŭ directly before a noun or noun-like expression.

A useful way to remember it is:

• antaŭ
  • noun/thing
• antaŭ ol
  • clause

Because after antaŭ ol, Esperanto normally uses the present tense for an action that is still in the future relative to the main situation, just as English says before you cross, not usually before you will cross.

So:

• antaŭ ol vi transiras = before you cross

This is the normal and natural choice here.

With a normal finite verb like transiras, Esperanto usually needs an explicit subject.

So:

• vi transiras = you cross

You cannot normally just say antaŭ ol transiras by itself, because transiras needs a subject.

If you wanted a subjectless form, you would usually switch to an infinitive construction instead, but this sentence chooses the full clause antaŭ ol vi transiras, which is very clear and natural.