Is community college (and then transferring to 4 year) only for general ed. classes?

For many common majors, you complete general education courses and frosh/soph level courses for your major. http://www.assist.org lists the major preparation courses that you need for a given major and target UC or CSU. Examples for a student at Santa Monica College:

UCLA psychology major: http://web2.assist.org/web-assist/report.do?agreement=aa&reportPath=REPORT_2&reportScript=Rep2.pl&event=19&dir=1&sia=SMCC&ria=UCB&ia=SMCC&oia=UCB&aay=16-17&ay=16-17&dora=PSYCH

UCR psychology major: http://web2.assist.org/web-assist/report.do?agreement=aa&reportPath=REPORT_2&reportScript=Rep2.pl&event=19&dir=1&sia=SMCC&ria=UCR&ia=SMCC&oia=UCR&aay=16-17&ay=16-17&dora=PSYC

CSULB psychology major: http://web2.assist.org/web-assist/report.do?agreement=aa&reportPath=REPORT_2&reportScript=Rep2.pl&event=19&dir=1&sia=SMCC&ria=CSULB&ia=SMCC&oia=CSULB&aay=16-17&ay=16-17&dora=PSYCH

CSULA psychology major: http://web2.assist.org/web-assist/report.do?agreement=aa&reportPath=REPORT_2&reportScript=Rep2.pl&event=19&dir=1&sia=SMCC&ria=CSULA&ia=SMCC&oia=CSULA&aay=16-17&ay=16-17&dora=PSY

Community college in California is inexpensive for California residents, and does not put the student on as strict of a clock in terms of needing to declare a major as quickly. This gives the undecided student more time to decide, since extra semesters at community college are less costly than extra semesters at a four year school.

Yes. As noted above, see http://www.assist.org for courses that you need to take for your intended major(s).

Yes. Note that if you select your courses carefully, the courses you take to prepare for your possible majors may also fulfill general education categories.