You can enter in any server, with any character. Except for the seasonal servers - they can be entered with a seasonal character.

Hello Elspeth, I understand you are confused with BDO's shared world system. Please know we are not quite like other MMO's! BDO is divided by Region. For example. The north america servers- this is one region, then the European servers, this is another region. BUT. In the region of Europe (EU) all the servers you see. For example, Kamasylvia, Balenos, Calpheon, etc. Your progress is shared across all of them! You are free to move between each and every server as you please as they are all in the same world system (Region)! You do not lose any progress going from server to server as long as it is in the same Region! The only exception is if you see Season 1-2-3-4 servers! These are exclusively for season characters who you create and then they graduate later on to join the rest of your characters in your family!