Answer 1

Core Java means the standard edition (Java SE) that covers all of the language features, as implemented by OpenJDK, Oracle JDK and others.

Advanced Java was earlier called Java Enterprise Edition, and on top of the core features it contained some extra functionality targeted for larger corporations, especially related to web services and distributed computing. This is now known as Jakarta EE, developed by the Eclipse Foundation and focused on cloud technology.

https://en.m.wikipedia.org/wiki/Java_Platform,_Enterprise_Edition

https://jakarta.ee/about/

Answer 2

Advanced Java isn't very much used these days so learning core java is worth your time you devote to it

Answer 3

Start from core java and then move to advance. Even most of the companies test you only on core Java for an entry level profile.