Mi petas, ne forgesu la bileton.

In Esperanto, -u is the verb ending for the command / request / wish form, often called the volitive.

So:

• forgesi = to forget
• forgesas = forgets / am forgetting
• forgesis = forgot
• forgesos = will forget
• forgesu = forget! / do forget / please forget / let someone forget

In ne forgesu, the -u form is being used for a polite negative request: don’t forget.

Because Esperanto uses ne + the -u form to make a negative command or request.

So:

• forgesu! = forget!
• ne forgesu! = don’t forget!

The infinitive forgesi means to forget, but infinitives are not used as commands.

Yes. Literally, Mi petas means I ask or I request.

But in sentences like this, it often works like English please. So:

• Mi petas, ne forgesu la bileton.

can be understood as a polite way to say:

• Please, don’t forget the ticket.

This is a fairly natural Esperanto way to make a request more polite.

It is one common way, but not the only one.

You may also see:

• Bonvolu ne forgesi la bileton. = Please don’t forget the ticket.
• Mi petas, ne forgesu la bileton.
• simply Ne forgesu la bileton, mi petas.

A learner should know that Esperanto does not have one single all-purpose word that matches English please perfectly in every situation. Mi petas is common and understandable, especially in requests.

The comma separates the polite introductory phrase from the main request.

So the structure is roughly:

• Mi petas, = please / I ask
• ne forgesu la bileton. = don’t forget the ticket.

This punctuation helps show that Mi petas is not the main action of the sentence in the usual sense, but more of a polite lead-in.

The -n ending marks the direct object in Esperanto.

Here, the thing being forgotten is the ticket, so la bileto becomes:

• la bileton

because it is the object of forgesu.

Compare:

• La bileto estas sur la tablo. = The ticket is on the table.
• Ne forgesu la bileton. = Don’t forget the ticket.

In the second sentence, the ticket is what is being forgotten, so it takes -n.

La means the.

In this sentence, la bileton suggests a specific ticket that both speaker and listener know about: for example, the ticket for the trip / concert / train.

If you said bileton without la, that would sound more like a ticket or some ticket, which is usually less natural in this context.

So ne forgesu la bileton is the normal way to say don’t forget the ticket.

Very often, yes. Forgesi is usually a transitive verb, meaning you forget something:

• forgesi la nomon = forget the name
• forgesi la ŝlosilojn = forget the keys
• forgesi la bileton = forget the ticket

You can also use it without an explicit object in some contexts, but in this sentence the object is clearly stated.

Yes. That is also possible.

Both of these are understandable:

• Mi petas, ne forgesu la bileton.
• Ne forgesu la bileton, mi petas.

The difference is mostly in style and emphasis. Putting Mi petas first gives the sentence a more immediate polite framing.

By itself, forgesu does not mark singular vs. plural the way some languages do. The -u form is used for a command or request, and the subject is often understood from context.

So it can mean:

• don’t forget said to one person
• don’t forget said to a group

If needed, Esperanto can make the subject explicit:

• Vi ne forgesu la bileton. = You, don’t forget the ticket.
• Vi ĉiuj ne forgesu la bileton. = All of you, don’t forget the ticket.

But usually the simple form is enough.

A simple pronunciation guide is:

• Mi ≈ mee
• petas ≈ PEH-tahs
• ne ≈ neh
• forgesu ≈ for-GEH-soo
• la ≈ lah
• bileton ≈ bee-LEH-ton

A few useful pronunciation points:

• Esperanto stress is usually on the second-to-last syllable:
  • PE-tas
  • for-GE-su
  • bi-LE-ton
• Each vowel is pronounced clearly.
• The g in forgesu is a hard g, as in go.

You could say Bonvolu ne forgesi la bileton, and it is understandable, but many speakers would more naturally say:

• Bonvolu ne forgesi la bileton or
• Mi petas, ne forgesu la bileton

The important point is that Esperanto often prefers the -u form for requests. So ne forgesu is a very central pattern to learn for don’t forget.

A literal word-for-word approach from English is not always the most natural, but in this case your version is still quite reasonable.