E codes are used during Printing progress
It denotes how much length of PLA or ABS to be extruded during Printing
Initially E codes are set to E0
E1.0000 denotes extrusion of 1mm PLA/ABS
if you need to extrude 1mm more then E code should be E2.0000
i.e., incrementing the values whenever you need the extrusion
if the next value is E1.5000 the extruder sucks back the PLA about 0.5mm
You can vary the Extrusion Multiplier in Printer settings and convert to Gcode to increment or decrement the Extrusion length in percentile during printing (It works during printing)