Adding to what everyone has mentioned here, newbie should not be confused with noob (Which happens a lot), for all intentions and purposes:
newbie should be considered a word that references a person that is new to something, inexperienced or otherwise lacks in that particular moment, the knowledge to do some tasks, activities or any other actions in a way that shows experience and knowledge about the usage of how the system in use works, be it a particular game (where it is used most often), a programming language or other activities where the user can gain experience over time.
noob on the other hand is the negative aspect that gets many users confused with newbie, this is mostly related to the pronunciation and environment where they are used. noob means a user who has at least one of the following characteristics and still does not appear to have gained experience over time:
- He/She has been a user of a particular system for a long time
- He/She has the knowledge of how the system works
- He/She is preconsidered an experienced user because of time spend on the system and supposed knowledge of it (Sorry for the preconsidered oxymoron)
Because of all of this, one would think the user knows about the system but after having some experience with the user, one finds out the user, with all of his/her time using the system and learning from it, has nothing to show for. Basically an "experienced user" with 0% learned. In this case, noob is used to denote that the user, with all of his/her time spend in said activity, game, task has not learned anything new or has nothing to show for.
So the basic difference is that newbie is only applied to a new user that is introduced to a system he/she does not know yet. noob is used when a user has already time spend on the system and has learned nothing yet.