When you socialize, you participate in activities in a group setting. If you have been studying alone for some time, you might take a break at the coffee shop to socialize with some friends.
You can socialize somebody else, or educate her in social patterns. Parents socialize their kids through their upbringing, and clubs often socialize their members through a uniform. If you want to hang out with motorcyclists, you might want to dress in leather. It is also possible to socialize institutions, where benefits are open to a wide section of society. If voters socialize medicine, that service becomes available to all at government expense.