Tango involves gathering with others to learn, explore and enjoy. Here are the formats that are the most common.
Classes: In classes, people learn in a group of anywhere from 2 and 100 learners, usually for 60-90 minutes under the direction of a teacher or pair of teachers. Classes may be labeled beginner, intermediate, or advanced; most are actually mixed in level since there is no agreement on what skills constitute different levels. Classes can be structured around different assumptions. For instance, some teachers assume that all the men in the class will lead and all the women will follow, others will assume that everyone will practice both roles, other classes may be designed a specific role ("Follower's Technique") or even gender (Men's Class). Some classes require participants to bring a partner; if they don't, teachers will often request participants to rotate; in some cases they will leave partnering up to the participants. Classes may be organized as "drop-in" or "series."
Practicas: Practicas are informal events where learners gather with the purpose of practicing. Sometimes people will plan in advance to practice with a specific partner for awhile, or they may plan short 15- and 30-minute 1:1 lessons with teachers. Sometimes practicas are facilitated by a host, who may suggest things to work or encourage people to work together. Practicas may include light snacks.
Private Lessons: Private lessons are 15- to 90-minute sessions for an individual or pair of any level of dance, with one or two teachers. These may happen in a private setting, or in a public setting where other lessons are also happening.
Milongas: A "milonga" is a tango party - a social gathering where people gather for the purpose of dancing Argentine tango, usually with a variety of partners. Milongas are hosted by organizers who are usually dancers dedicated to tango and trying to build community. There is often a DJ who plays music in sets of similar music, or "tandas." It is a custom to invite someone to dance in the first or second song of a tanda, and dance all the rest of the songs in the set with that person. At the end of the tanda, dancers part ways or decide to do a second tanda. Anyone may invite any other person to dance. Some people enjoy the Argentine tradition of "cabeceo," or inviting via an eye-contact gesture. Sometimes, there are improvised or choreographed performances. The last song of a milonga is by tradition, "La Cumparsita." Milongas may happen in the morning, afternoon, evening, or night and may take place indoors or outdoors. Milongas usually have a certain frequency, e.g., weekly, monthly (for instance, the 1st Friday of the month), or quarterly.
Workshops: Sometimes, Tango professionals may offer a special one-off class in an area of speciality or interest. They are usually longer than classes: 75-90 minutes or even longer, and they vary quite a bit. They are very similar to classes.
Competitions: Competitions are events in which some dancers sign up to be judged by other tango dancers. They often include the elements of a festival.
Festivals: Festivals are weekend-long events made for dancers from the region, nation or world for a variety of tango-related experiences: workshops, practicas, milongas, and private lessons. Often there are also tango vendors who sell apparel and shoes. The professionals teaching workshops at the festival will often give performances during the milongas. Festivals tend to happen annually, e.g, the 12th Annual San Diego Tango Festival.
Marathons: Marathons are weekend-long events that bring together dancers from the region, nation or world specifically for social dancing at milongas. There may be a small number of workshops, communal eating events, or group discussions, but the main substance of the marathon is dancing at daytime and evening milongas. Some marathons are invitation-only, and some focus on a specific kind of dancing, e.g., "Encuentros" which focus on what they call "milonguero-style."