The rules for negation are much as in English.
Vi nek sidas nek rigardas. – You are neither sitting nor looking.
Mi neniam diros al iu. – I shall never tell anyone. (Mi neniam diros al neniu is wrong in Esperanto just as "I shan't never tell no-one" is in English.)
Mem means "self" (myself, yourself, himself etc.) and is used to emphasize the noun or pronoun it follows. (Compare si, reflexive, lesson 4.)
There are various ways of saying "goodbye" in Esperanto, but the most usual is
Alternatively it may be said without the article:
means "thing", a concrete object: