The "electric field" is a vector field that, at each point, if multiplied by a charge, gives the force vector on that charge at that point.
If you have q1 at point A, charge q2 at point B, charge q3 at point C, etc., then the electric field at point P is the sum of forces on a unit charge by charges q1, q2, and q3.
Letting V1 be the vector from point P to A, The force on the unit charge at P due to charge q1 is q1V1/V1, where V1 is the length of vector V1. Similarly if V2 is the vector from point P to B, the charge on the unit charge at P due to charge q2 is q2V2/V2 and if V3 is the vector from point P to C, the charge on the unit charge at P due to charge q3 is q3V3/V3.
The electric field due to all three charges, at point P, is the vector sum q1V1/V1+ q2V2/V2+ q3V3/V3.
