Enable is the clocking signal for writing and reading. Normally E is low when nothing is accessing the display.
To write data or command, put the data byte on the port pins, then take E from low to high, and keep it high for 500 nS or longer. Then take E low again. The data is clocked into the display on the falling edge of E. Do not do another write until 1 uS has elapsed. That means you may have to use a delay while the E is high, and again after it goes low, to meet the timing minimums.
Do you need the explanation for reading?
This info is on pg 9 of the data sheet, and you are good at reading data sheets, right?