Calculating resultant force is the diagonal of the shape made by the vector
A scalar is a quantity that only has a magnitude (so it can only be positive) for example speed.
A vector quantity has a direction as well as a magnitude, for example velocity, which can be negative.
A parallelogram has to be made with the acting forces (F1 and F2). The resultant force will be the diagonal. Make sure the same scale is used to convert between length and forces. Measure length of diagonal and use scale to convert value into force (FR).