Mia kolegino akceptis mian inviton, sed ŝia frato rifuzis ĝin.

The suffix -in- marks a female person.

• kolego = colleague, coworker
• kolegino = female colleague, female coworker

So mia kolegino means my female colleague. The ending -o shows it is a noun.

You can see the same pattern in:

• frato = brother
• fratino = sister

In Esperanto, -is is the past-tense verb ending.

• akceptas = accepts

• akceptis = accepted

• rifuzas = refuses
• rifuzis = refused

So both actions happened in the past:

• akceptis = accepted
• rifuzis = refused

One nice feature of Esperanto is that verb endings are very regular:

• -as = present
• -is = past
• -os = future

The ending -n marks the direct object in Esperanto.

A direct object is the thing that receives the action.

In this sentence:

• Mia kolegino akceptis mian inviton

  • mia kolegino = the subject, the person doing the action
  • mian inviton = the thing being accepted, so it gets -n

• ŝia frato rifuzis ĝin

  • ŝia frato = the subject
  • ĝin = the thing being refused, so it also gets -n

So:

• invito = invitation
• inviton = invitation as a direct object
• ĝi = it
• ĝin = it as a direct object

Because both the adjective and the noun must match.

In Esperanto, adjectives agree with the nouns they describe in:

• number
• case

Here, inviton is a direct object, so it has -n. The possessive adjective mian must match it.

So:

• mia invito = my invitation
• mian inviton = my invitation as a direct object

This agreement is very important in Esperanto.

They work like English my, his, her, and so on.

• mia = my
• ŝia = her

So:

• mia kolegino = my female colleague
• mian inviton = my invitation
• ŝia frato = her brother

Notice that ŝia does not take -n here, because frato is the subject, not the object.

If frato were a direct object, then both would change:

• mi vidis ŝian fraton = I saw her brother

ĝin means it, and here it refers back to mian inviton.

So the second clause means:

• ŝia frato rifuzis ĝin = her brother refused it

Using ĝin avoids repeating mian inviton.

You could also say:

• ŝia frato rifuzis mian inviton

But ĝin sounds more natural because the invitation has already been mentioned.

Because the pronoun refers to inviton, which is a thing, not a person.

In Esperanto:

• li / lin = he / him
• ŝi / ŝin = she / her
• ĝi / ĝin = it

Since the invitation is not a person, Esperanto uses ĝi. Because it is the direct object of rifuzis, it becomes ĝin.

Sed means but.

It connects two contrasting ideas:

• Mia kolegino akceptis mian inviton
• sed ŝia frato rifuzis ĝin

So the contrast is:

• my female colleague accepted the invitation,
• but her brother refused it.

Esperanto has:

• la = the
• no indefinite article for a/an

So Esperanto often simply leaves out a/an.

Also, when a noun already has a possessive word like mia or ŝia, you normally do not use la with it.

So:

• mia kolegino = my colleague
• mian inviton = my invitation
• ŝia frato = her brother

These are already specific because of the possessives, so la is not needed.

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

The normal order here is:

• subject + verb + object

So:

• Mia kolegino akceptis mian inviton

But because mian inviton has -n, it is still recognizable as the object even if moved.

For example, you could say:

• Mian inviton akceptis mia kolegino

That is grammatical, though it may sound more marked or emphatic.

The original version is the most neutral and natural for most situations.

These are special Esperanto letters.

• ŝ sounds like English sh in ship
• ĝ sounds like the j in jam

So:

• ŝia sounds roughly like SHEE-a
• ĝin sounds roughly like jeen

Esperanto spelling is very regular, so each letter has a consistent sound.