you just bought a real estate interest in a teeny-weeny piece of unit 6a (whatever that is) at VWL. unit 6a might be a studio or something else...not really important. (unless unit 6a catches on fire...in which case your ability to use DVC might be impaired.)
Legally, you own an interest in a particular unit. When a DVC resort is constructed, it is divided into "units" that are normally groups of rooms. DVC declares one or more of these units into the "DVC Association" and sales begin. As sales progress and "units" sell out, more units are declared into the association, and sales begin on those units.
Units that have not yet been declared into the association are the property of Disney Vacation Development, and can be rented for cash reservations or used for promotions like giveaways and "developers points."
In practice, you may never stay in the actual "unit" you own. For instance, if half of the units at BLT are declared into inventory, and half are undeclared, the entire resort is open for reservations, but 50% of the rooms will be available for point reservations and 50% for cash reservations.