Mi donas la libron al mia fratino.

Donas is a conjugated verb: it means give / am giving / do give in the present tense.

• doni = to give (the infinitive)
• donas = gives / am giving / give (present tense)

Because the subject is Mi (I), the sentence needs a finite verb, so donas is the correct form.

The -n ending marks the direct object in Esperanto.

In this sentence, the thing being given is the book, so la libro becomes la libron.

• libro = book
• libron = book as the direct object

A useful question is: What is being given?
Answer: the book.
So it gets -n.

Because mia fratino is not the direct object here. It is the recipient, introduced by the preposition al.

• al = to
• al mia fratino = to my sister

In Esperanto, a noun after a preposition usually does not take -n unless there is some special reason, and here there is not.

So:

• la libron = direct object → takes -n
• al mia fratino = prepositional phrase → no -n

Al means to and shows the receiver or direction toward someone/something.

In Mi donas la libron al mia fratino, it tells you who receives the book:

• Mi = the giver
• la libron = the thing given
• al mia fratino = the receiver

This is very common with doni:

• doni ion al iu = to give something to someone

Because the whole phrase al mia fratino is governed by the preposition al, so it does not need the accusative -n.

Also, mia behaves like an adjective, so if the noun had -n, mia would match it:

• mian fratinon = my sister as a direct object

But here that is not the role. Here it is simply:

• al mia fratino = to my sister

So both words stay without -n.

La is the definite article, meaning the.

Esperanto has only one article:

• la = the

There is no indefinite article for a/an. So:

• libro can mean a book or just book
• la libro means the book

In this sentence, la libron means a specific book, not just any book.

No. Esperanto verbs do not change according to the subject.

So:

• mi donas = I give
• vi donas = you give
• li donas = he gives
• ŝi donas = she gives
• ili donas = they give

The ending -as always marks the present tense.

This is often much simpler for English speakers, because you do not have to memorize forms like give/gives.

It can cover all of those, depending on context.

Esperanto present tense -as is broader than a single English form. So mi donas can mean:

• I give
• I am giving
• I do give

Usually the situation makes the meaning clear.

If you need to emphasize ongoing action, you normally do it with context or extra words rather than a special verb form.

Not completely. Esperanto word order is fairly flexible because endings show the grammatical roles.

The most neutral order is:

• Mi donas la libron al mia fratino.

But you may also see:

• Al mia fratino mi donas la libron.
• La libron mi donas al mia fratino.

These variations can change emphasis, but the grammar is still clear because:

• libron has -n, so it is the direct object
• al mia fratino shows the recipient

Still, for learners, the original order is the safest and most natural.

In normal Esperanto with doni, you should use al for the recipient:

• Mi donas la libron al mia fratino.

That is the standard, clear pattern:
doni ion al iu = to give something to someone

Using al is the normal and recommended way.

• mi = I
• mia = my

So:

• Mi donas... = I give...
• mia fratino = my sister

This is similar to English:

• I vs my
• he vs his
• she vs her

In Esperanto, possessive words like mia, via, lia, ŝia, etc. act like adjectives.

Fratino means sister.

It is built from:

• frat- = sibling / brother-sister root
• -in- = female suffix
• -o = noun ending

So:

• frato = brother
• fratino = sister

This is a very common Esperanto pattern:

• patro = father
• patrino = mother

You would make the noun plural with -j:

• al miaj fratinoj = to my sisters

Notice that the possessive adjective agrees too:

• mia fratino = my sister
• miaj fratinoj = my sisters

So the full sentence would be:

• Mi donas la libron al miaj fratinoj.

If there were more than one book too, then:

• la librojn = the books

The subject is usually the noun or pronoun doing the action, and here it is Mi.

You can identify the parts like this:

• Mi = subject, the one doing the giving
• donas = verb
• la libron = direct object, the thing given
• al mia fratino = recipient, the one receiving it

So Mi is the subject because I am the one performing the action.

Yes, but the meaning changes slightly.

• Mi donas la libron al mia fratino. = I give the book to my sister.
• Mi donas libron al mia fratino. = I give a book to my sister / I am giving a book to my sister.

Without la, the noun is less specific.

Because Esperanto has no separate word for a/an, the bare noun often does that job.

Only the verb ending changes.

• Mi donas la libron al mia fratino. = present
• Mi donis la libron al mia fratino. = past
• Mi donos la libron al mia fratino. = future

Very regular endings:

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

Everything else can stay the same.