How does one learns tango? In the past, people would just ask friends and family members to show them, then they would go to milongas and watch.  They would practice privately with friends/family, and at some point try to dance in milongas. You can still do that, but you will need a lot of time.

Today, tango is taught primarily in group classes. When conditions/resources allow, private classes are also used to allow a teacher to concentrate on a single student.