How to compute secure sum using secure multparty computation?
In general, there are many techniques for secure multiparty computation. However, the problem of voting is much broader than this, and if you are really interested I suggest looking into the voting literature in depth.

One of the big questions is the model: typically, you cannot run a regular MPC protocol since that requires interaction among all the parties. One solution (which is an old work, but one that I really like), separates between an election service provider and the actual election being held. Actually the work talks about auctions, but a similar idea can be used. See Privacy Preserving Auctions and Mechanism Design.

For more modern work on elections, see Helios (which is the scheme used by the IACR). I suggest looking at Wikipedia - end-to-end verifiable voting for some sources, but note that a lot of research is needed. In general, secure tallying is a tiny part of what is needed for a real election (and the easiest to solve).