Pulling EN-Latch low takes in the address on pins A0-A3 and latches it. Each of these have an X in the lookup table box for the bit position they control. The Y pins have a corresponding table where the black boxes are Boolean 1/address pin high values. The output enable pin sets the previously latched addressed Y pin high. This chip is typically used as glue logic for selecting peripheral circuits, like when extending memory beyond the address space available to a processor. So if 64k is the whole address range, and the 74HC4514 is connected with every Y pin connected to the chip enable(s) of an additional 64k of mapped memory, it is possible to address over 1 megabyte.