There are many and very diverse migrant organizations in Germany. These organizations are often founded by people with a migration background; the majority of members are migrants. Migrant organizations have different interests, services, and goals. Some advise and support people who are new to Germany. Others focus on maintaining the language and culture of their origins. Still others are involved in youth and/or adult education, for example.
Some migrant organizations have a highly structured structure, while others are more loosely organized initiatives and volunteer associations. There are also online communities: these are groups where migrants exchange ideas online on various topics. You can become a member of a migrant organization, but most organizations don't require you to be a member to use their services.