What constitutes the mass of electron? Electron has mass of $9.10938356 \times 10^{-31}$ kilograms. Since an electron has mass, it should be made of some material. I understood that electron is nothing but negative charge. If this is the case what constitutes the mass of electron since charge does not contain mass? What is an electron made of in terms of matter (not as charge)?
 A: The electron is an elementary point  particle in the standard model of particle physics, .
This model is very successful in describing and predicting elementary particle interactions using quantum field theory.
The mass you require, " some material", is a macroscopic concept, and macroscopic material emerges from the underlying quantum mechanical which is modeled so successfully with the electron a point particle with mass and charge.
Macroscopically mass is defined by the concept of resistance to force , F=ma . Force at the quantum level is just dp/dt, the change of momentum in interactions, and the successful fit and predictions of the standard model means that yes, point particles can resist acceleration, consistent with the concept of their having a fixed mass.
If you look at the table some of the point particles have masses much larger than the one of the electron.
A: The straightforward answer is that nobody knows. The explanation that electron mass is generated by its coupling to the Higgs potential leaves the question to what the Higgs field is coupled and why with the coupling constant that is observed. 
