APEX

I searched, but couldn't seem to find if this question had already been answered.

I just picked up beginning oracle application express by wrox.

I came to oracle and downloaded Oracle Database XE then went to search for apex.

Installed Oracle Database XE ..signing is as system your options appear to be administration, object browser, sql, and utilities.
unlocked the HR sample user account and logged in..it has the same options above, but also application builder.

So, I guess my question is..

1. why does HR have application builder, but system does not?
2. do you need to download and install Apex or is apex already preinstalled using Oracle Database XE?
3. is Apex the same thing as application builder or are they completely different.

Thank you for you answers

Thomas