The historical Buddha, Shakyamuni, is quoted in the Upaddha Sutra as having said that dharma friendships are the whole of our spiritual life. In the Sutra he goes on to say that just as his students have depended on him for spiritual friendship, and have thereby been able to pursue the Noble Eightfold Path of practice, so too each of us depends on our spiritual friends to help us walk the path. This is a teaching about sangha. It means that the Buddha and Ananda, our Dharma teachers, and all of our fellow practitioners are our personal sangha.
But what is it that makes a sangha? Each one of us might have a different answer to this question. Originally, in the Buddha's time, Sangha meant the community of women and men who were ordained as nuns and monks. At that time, ordination was sometimes as simple as the Buddha saying, "Come monk." Still there was a strong sense of renunciation, and a person took on a difference appearance and lifestyle when they became part of the early Sangha.
Over the centuries various Buddhist traditions have evolved from the historical Buddha's teachings and, in modern day Zen, sangha is understood to mean the fourfold sangha of lay women, lay men, ordained women and ordained men. Thus, anyone who is a Zen practitioner is part of the Zen sangha. It can include people of any age, any background, any culture or skin color, and any amount of practice experience.
For me, sangha means the people who share an intention to live an awakening life, a life that returns again and again to the work of bringing compassion and wisdom into our hearts and into the world. Without this shared intention and the actions that make it come alive, we cannot really call ourselves part of a sangha. Both things are necessary - the intention and the action. It is work, but it is the most worthwhile kind of work you can do if you want to have peace of mind.
Thus, taking refuge in sangha is one of the key vows of a Buddhist. You may appreciate the teaching of Buddhism, and that may or may not make you a Buddhist. You may enjoy the people, places and things associated with Buddhist practice, and that may or may not make you a Buddhist. To take refuge is to turn for guidance to Buddha understood as awakened nature, the Dharma understood as the teachings, and the Sangha understood as the people who make these teachings present in the world. Once you take refuge, then you are ready to take the vows.