Lord Tirian has it right. A burst X radiates out X squares in all directions from a single, central square, which is either your square (close burst) or a square within a specified range (area burst).
A close blast X is a square area X squares on a side, at least one square of which must be adjacent to you. We haven't seen anything to indicate that there's such a thing as a ranged blast, but if there is, presumably it would follow the same rule: one square of the blast would have to be adjacent to the origin square.
Note that this means a burst 5, for example, is actually slightly more than twice as large as a blast 5. A burst 5 would be 11 squares on a side (five squares in each direction, plus the originating square), while the blast 5 is 5 squares on a side.