Se estas glacio sur la vojo, ni devas iri malrapide.

Esperanto does not use a dummy subject like English there in sentences such as there is or there are.

So:

• Estas glacio. = There is ice.
• Estas problemo. = There is a problem.

Literally, estas glacio looks like is ice, but in normal Esperanto this is the standard way to express existence.

Yes. Se means if and introduces a condition.

So:

• Se estas glacio sur la vojo... = If there is ice on the road...

Esperanto does not change the verb form after se the way English sometimes does in more complicated conditionals. In a simple sentence like this, it works very much like English if.

The comma separates the if-clause from the main clause:

• Se estas glacio sur la vojo, = conditional clause
• ni devas iri malrapide. = main clause

This is very common and natural in Esperanto, especially when the subordinate clause comes first.

Sur means on, while en means in.

Here, sur la vojo means on the road / on the surface of the road, which is what you want for ice.

• sur la vojo = on the road
• en la vojo = in the road / in the way

So sur is the natural choice when talking about ice lying on the road surface.

La means the.

In this sentence, la vojo refers to a specific road in the situation being discussed, or simply the road in a general real-world sense.

• sur vojo would sound more like on a road
• sur la vojo means on the road

Esperanto uses la when the noun is definite, much like English.

After modal-type verbs like devi (must / have to), Esperanto uses the infinitive directly, with no separate word meaning English infinitive to.

So:

• devas iri = must go / have to go
• not something like devas to go

This is normal Esperanto structure:

• Mi volas iri. = I want to go.
• Ni povas veni. = We can come.
• Ni devas iri. = We must go.

Because it describes how we go, it has to be an adverb, not an adjective.

• malrapida = slow (adjective, describes a noun)
• malrapide = slowly (adverb, describes a verb)

Here it modifies iri (to go), so:

• iri malrapide = to go slowly

Also, mal- is a very common Esperanto prefix meaning the opposite of:

• rapida = fast
• malrapida = slow

It can mean either must or have to, depending on context.

• ni devas iri malrapide can mean we must go slowly
• or we have to go slowly

In this sentence, it expresses necessity or obligation because of the icy road.

Esperanto verbs do not change according to person or number.

So the present tense ending is always -as:

• mi devas = I must
• vi devas = you must
• li devas = he must
• ni devas = we must
• ili devas = they must

This is one of the simpler parts of Esperanto grammar.

Yes. Esperanto word order is fairly flexible, as long as the grammar stays clear.

For example, you could also say:

• Ni devas iri malrapide, se estas glacio sur la vojo.

That still means the same thing: We must go slowly if there is ice on the road.

The original version puts the condition first, which often feels natural: first the situation, then the result.

Literally, iri means to go, so the sentence is somewhat general.

Depending on context, ni devas iri malrapide could mean:

• we must walk slowly
• we must drive slowly
• we must proceed slowly

If the meaning shown to the learner is about traffic or travel, the idea is probably we must go slowly in a general sense, not necessarily only walking.

Yes. That would also be natural.

• ni devas = we must
• oni devas = one must / people must / you must in a general sense

So:

• Se estas glacio sur la vojo, oni devas iri malrapide. means something like If there is ice on the road, one must go slowly or people have to go slowly.

The original sentence with ni is more specific and includes the speaker: we.