It's similar to a Christian wearing the Cross or Crucifix or a Jew wearing the Star of David. Most Wiccans meet with a coven, a small group of people. Each coven is autonomous. Most are headed by a High Priestess, often with the assistance of a High Priest. Some are headed by a High Priestess or High Priest without a partner, and some regard themselves as a gathering of equals.
Covens can be of mixed gender, or all female or male, depending on the preferences of the members.
Every initiate is considered to be a priestess or a priest. Most covens are small. Thirteen is the traditional maximum number of members, although not an absolute limit. At that size, covens form a close bond, so Wiccans in the military are likely to maintain a strong affiliation with their covens back home. A typical difference would be that more traditional groups would tend to follow a set liturgy, whereas eclectic groups would emphasize immediate inspiration in worship.