Is enrolling in Army ROTC the same as joining the Army? Once a student starts taking ROTC courses, is he/she obligated to join the Army?

Enrolling in Army ROTC is not, strictly speaking, joining the Army. You will not be sent to boot camp. However, the primary purpose of the Army ROTC program is to produce its Officers, so you must agree to serve as Officers in the Army after graduation in order to go through the entire program, or if you have received an ROTC scholarship. Enrolling in the ​ROTC Basic Course​ (the first two years of college) does NOT obligate you to serve unless you have also received a scholarship.