For every new character you create, they begin life at the start of the game, but the other current character(s) on your same account remain unaffected. For example, you can create your first character and take them to Post-Searing, then create a new character and leave them in Pre-Searing - your first character remains unaffected in Post. Most players have at least two characters (I have eight across two accounts), and use their Post-Searing characters to stock up on better arms and armor for when they bring their newer ones to the Post-Searing world.
You can re-use names for any character you delete from your account. I believe the devs have any names you use reserved for your account for 60 days after you delete a character so no one else has access to that name for that period of time in case you wish to re-use it. This might be a carry-over from the beta events, though. I actually haven't tried using the same name from one account on the other, but will try next time just to see what happens.
Hanok Odbrook
Real Millennium Group Guild
http://www.realmillenniumgroup.com/guild.html
Truth * Knowledge * Peace