Saluton!

I'm new to this forum and new to Esperanto so sorry if this is an obvious question.

My first Esperanto "study guide" was the phrases on this website: http://omniglot.com/language/phrases/esperanto.php

After reading about grammar I was confused about some of the phrases that end in -on which I thought was the accusative noun ending.

Saluton / Helpon / Dankon.

My guess is that these phrases are abbreviated for longer ones like "Mi bezonas helpon" => "Helpon". Would "helpu" have the same meaning?

Oops. I just read another post on this forum saying that it's for questions in Esperanto. I'll move this over to the English forum.