Bear in mind that these concurrent interests are not ways to divide property spatially. In each, all of the co-owners have the equal right to possess all of the property. Tenancy in common is the most basic of the concurrent interests. Each tenant in common has a separate interest in the property, which he can dispose of as he chooses. If B dies, and in his will gives his interest to D, now C and D are tenants in common.
Joint tenancy is just the same, with one big exception.
That is, when one dies, the other automatically gets his interest. If A and B are joint tenants, and A dies, B gets A's interest regardless of what A's will says. Joint tenancy is useful because it keeps the property out of probate, which saves time and money. To create a joint tenancy, the tenants must acquire their interests at the same time, through the same instrument, and each tenant must have an equal interest. Tenancy by the entirety is like joint tenancy, but is available only to married couples, and cannot be severed unilaterally by one party.