Se ni alvenos ĝustatempe, ni povos komenci la kunvenon.

This is a very common question. In Esperanto, it is normal to use -os in the se-clause if the meaning is future.

So:

• Se ni alvenos ĝustatempe = If we arrive / will arrive on time
• ni povos komenci la kunvenon = we will be able to start the meeting

English usually avoids will after if, but Esperanto does not follow that rule. Esperanto tends to show the time more directly with the verb ending.

So this sentence is completely natural Esperanto.

Se means if.

It introduces a condition:

• Se ni alvenos ĝustatempe... = If we arrive on time...

You can think of se as the standard word for if in conditional sentences.

Alvenos means will arrive.

It is made of:

• alven- = the verb root meaning arrive
• -os = future tense

So:

• alveni = to arrive
• alvenas = arrive / am arriving / do arrive
• alvenis = arrived
• alvenos = will arrive

Esperanto verb endings are very regular, so once you know -os, you can recognize the future tense easily.

Ĝustatempe means on time or at the right time.

It is built from the idea of:

• ĝusta = correct, exact, right
• tempo = time
• -e = adverb ending

So the whole word gives the sense in a timely/correct-time way, which English expresses as on time.

Esperanto often combines ideas into one compact word where English uses a phrase.

Ĝ is pronounced like the g in judge.

So ĝustatempe begins roughly like:

• JUS-ta-TEM-pe

More precisely:

• ĝus sounds like joosh or jussh, depending on accent
• stress in Esperanto is always on the second-to-last syllable, so ĝustaTEMpe

That stress rule is very helpful:

• ĝus-ta-tem-pe
• stress on tem

Because povi means to be able / can, and it is followed by an infinitive.

So:

• povos = will be able
• komenci = to start

Together:

• ni povos komenci = we will be able to start

This works much like English:

• We will be able to start
• We can start

In Esperanto, after povi, the next verb stays in the infinitive form, usually ending in -i.

Because la kunvenon is the direct object of komenci.

In Esperanto, direct objects take the ending -n.

So:

• la kunveno = the meeting as a subject or basic noun form
• la kunvenon = the meeting as the thing being started

Since the sentence means start the meeting, the meeting receives the action, so it takes -n.

The base form is kunveno, which means meeting.

It comes from:

• kun- = together
• veni = to come

So the literal idea is something like a coming together, which becomes meeting.

In the sentence, it appears as kunvenon because of the direct object ending -n.

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

For example, this is also correct:

• Ni povos komenci la kunvenon, se ni alvenos ĝustatempe.

Both versions mean the same thing. The original puts the condition first, which is very natural:

• Se ni alvenos ĝustatempe, ni povos komenci la kunvenon.

That structure emphasizes the condition before giving the result.

Not if you mean a real future possibility like in the original sentence.

• alvenos = will arrive → a real future condition
• alvenus = would arrive → a more hypothetical or less real condition

So:

• Se ni alvenos ĝustatempe, ni povos komenci la kunvenon. = If we arrive on time, we will be able to start the meeting.

But:

• Se ni alvenus ĝustatempe, ni povus komenci la kunvenon. = If we were to arrive on time, we could start the meeting.

That second version sounds more hypothetical.

In this sentence, ni simply means we.

One thing to note is that Esperanto normally uses just one word, ni, for we. It does not usually distinguish between:

• we including you
• we not including you

English also usually uses just we, so this will feel familiar. The exact meaning depends on context.

Yes, depending on the nuance.

For example:

• ĝustatempe = on time / punctually
• akurate = punctually, accurately
• frue = early

But ĝustatempe is a very good choice here because it means arriving at the proper time, not necessarily early.

So in this sentence, ĝustatempe matches on time very well.