If I wanted to be a social worker, how many years of college would I need? And what kind of classes would I have to take?

A bachelor's degree in Social Work is generally a four year program. You have your general class requirements that everyone has when going to college. Other curriculum courses could look like the following, but may not be exactly as the following is stated. It does give you an idea of what to expect:

SOWK 105 Social Welfare Institutions
SOWK 147 Human Diversity
SOWK 151 Introduction to Social Work
SOWK 293 A-Z Special Topics
SOWK 300 Social Welfare Policy and Services1
SOWK 310 Social Welfare Policy & Services2
SOWK 319 Skills Lab 1
SOWK 320 Social Work Methods 1
SOWK 321 Field Expeience in Social Work
SOWK 322 Social Work Methods 2
SOWK 330 Human Behavior in the Social Environment 1
SOWK 350 Human Behavior in the Social Environment 2
SOWK 360 Social Work Research & Statistics
SOWK 491 Professional Field Placement
SOWK 493 A-Z Special Topics
SOWK 494 Seminar: Field Practice
SOWK 495 Independent Study

See also these sites:

Social Work Curriculum

Social Work Curriculum - KU School of Social Welfare

School of Social Work - Curriculum

You will have to have a BS (BA) for sure and will need a Masters normally.