The process of reaching voters is a process that has two important steps. The first step is identifying which voters to contact while the second step is actually contacting those voters and getting them to vote.
Perhaps the most important aspect of this process is identifying the voters to contact. Candidates do not want to waste their resources targeting voters who are not likely to vote for them or who are guaranteed to vote for them. Contacting either would be a waste of time and resources. Therefore, candidates use elaborate computer models to determine which voters might vote for them and might also need to be encouraged to do so.
Once they have figured this out, it is mostly just a matter of effort as opposed to a matter of figuring things out. The campaigns need teams of volunteers who will contact as many potential voters as possible by phone. For example, Mitt Romney’s organization was supposed to (but largely failed to due to technical problems) have people at polling places finding out who had voted and calling potential voters who had yet to vote.
Thus, the process of contacting voters consists first of figuring out which voters to contact and then of massive (largely volunteer) efforts to contact those voters and encourage them to vote.