Kuŝante sur la lito, mi legas libron.

Kuŝante comes from the verb kuŝi = to lie (in the sense of to be lying down).

It is made of:

• kuŝ- = the root
• -ant- = present active participle, meaning doing
• -e = adverb ending

So kuŝante literally means something like while lying or being in the state of lying down.

In this sentence, Kuŝante sur la lito, mi legas libron means that the reading happens while the speaker is lying on the bed.

Because here it functions adverbially, not adjectivally.

• -a makes an adjective: kuŝanta = lying as a description of a noun
  
  • for example: la kuŝanta viro = the lying man / the man who is lying down
• -e makes an adverb: kuŝante = while lying

In your sentence, the word is not describing a noun like man or book. It describes the action mi legas and gives the circumstance under which the reading happens. So -e is the correct ending.

Yes, normally it does.

In Esperanto, an adverbial participle like kuŝante usually has the same understood subject as the main clause. So:

• Kuŝante sur la lito, mi legas libron.

naturally means:

• While lying on the bed, I read a book.

The person lying down is the same person as the one reading: mi.

A learner should be careful with this. If the subject were different, the sentence could become confusing or wrong. Esperanto generally expects this construction to refer back to the main subject.

The comma separates the introductory participial phrase from the main clause:

• Kuŝante sur la lito, = introductory phrase
• mi legas libron = main clause

This is very similar to English punctuation in sentences like:

• Lying on the bed, I read a book.

The comma helps readability. In practice, Esperanto punctuation can be somewhat flexible, but using a comma here is very normal and helpful.

Because sur la lito expresses location, not direction.

• sur la lito = on the bed (already there)
• sur la liton = onto the bed (movement toward it)

In this sentence, the speaker is already lying on the bed, so it is a location. That is why lito does not take -n here.

This is a very common Esperanto pattern:

• no -n after a preposition for simple location
• -n can appear after a preposition to show direction or motion toward a place

Because libron is the direct object of legas.

• mi legas = I read
• libron = a book, the thing being read

In Esperanto, the direct object usually gets -n. So:

• mi legas libron
• ŝi vidas hundon
• ni manĝas panon

That -n ending is one of the most important markers in Esperanto grammar.

Esperanto has:

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

So:

• la lito = the bed
• libro / libron = a book or just book, depending on context

That means libron can naturally mean a book without needing any separate word.

The sentence uses la lito because it refers to a specific bed, or a bed assumed to be known from context.

Yes, that is possible.

Esperanto word order is fairly flexible, because endings show grammatical roles clearly. So these are all understandable:

• Kuŝante sur la lito, mi legas libron.
• Mi legas libron kuŝante sur la lito.
• Mi, kuŝante sur la lito, legas libron.

The version with Kuŝante sur la lito at the beginning puts more emphasis on the circumstance first: while lying on the bed.

So the original sentence is very natural, but it is not the only possible order.

Not exactly.

Kuŝi usually means to be lying down, not the action of going from standing/sitting to lying.

So:

• kuŝi = to lie / to be lying
• kuŝiĝi = to lie down / to get into a lying position

That means kuŝante here means while lying or while being in a lying position, not necessarily while lying down in the sense of the movement.

A simple way to remember it is:

• kuŝanta describes a noun
• kuŝante describes an action or the whole situation

Examples:

• La kuŝanta hundo dormas.
  = The dog that is lying down is sleeping.
  Here kuŝanta describes hundo.

• Kuŝante sur la lito, mi dormas.
  = While lying on the bed, I sleep.
  Here kuŝante describes how the action happens.

If you used kuŝanta in your sentence, it would not fit the grammar, because there is no noun for it to modify.

Yes, that is a very natural English rendering.

Literally, the Esperanto says something like:

• While lying on the bed, I read/am reading a book.

In normal English, a smoother translation might be:

• I’m reading a book lying on the bed.
• I’m reading a book while lying on the bed.
• I’m reading a book in bed.

The Esperanto participial phrase gives the idea of the speaker’s physical position during the reading.

It can mean both, depending on context.

Esperanto has a simple present tense:

• legas = read / am reading / do read

So:

• mi legas libron can mean
  • I read a book
  • I am reading a book

The exact English tense depends on the situation. In this sentence, because it describes a current ongoing posture (kuŝante sur la lito), English often prefers I am reading a book.

It is generally clear and natural.

The main thing a learner should know is the subject rule: kuŝante is understood to refer to mi. As long as that is your meaning, the sentence is good.

If you wanted to be even more explicitly natural in some contexts, you could also say:

• Mi legas libron, kuŝante sur la lito.
• Mi kuŝas sur la lito kaj legas libron.

The second version is more straightforward and less compact: I am lying on the bed and reading a book. But the original sentence is perfectly normal Esperanto.