When CE is false (low), the outputs and inputs are in tri-state or high impedance, it is as if the chip were not there. In fact the chip goes into a low power state for minimum drain on the supply. Micro amps of drain is common in this mode.
CE must be true (high) for the device to operate.
OE or Output Enable allows for the address bus (and select logic) to access the device without causing data to appear on the data bus. Think of an EEPROM which is being written, you would not want the data, which is being changed, to be available until the write operation is finished.