After playing with the beginner box what do I need to take my character to a core rulebook game? Do I have to modify the character sheet or do I have to learn new rules or I can just start playing exactly as I do in the beginner box and just level up?
I ask because I did have a bad experience with a DND beginner box long ago! After playing I discover that the core rulebook was a completely different game.
Core is the same game, albeit with more options though. Additional rules as well. I have seen success first hand by having the player create a new character using information from the existing PFBB character as reference and just following the leveling steps in Core.
For semi-new players, Core can be very intimidating. Just have them go slow.
The game itself is the same. The core rules just adds new options. The two options you'd probably want to know about are Five Foot Steps and Attacks of Opportunity.
Other than that, you know everything you need to know to play.
Are you joining somebody's game? Tell me that you're a BB player. You could play your existing BB character (and character sheet) in a normal game.
Are you looking to play Pathfinder Society games at a convention or game store? Then see this guide for converting to that: