Yes, the overall winner is quite simply the person who takes the least time to cover the whole distance, which is just over 2,000 miles. However, there are lots of other things going on to make the race more interesting; competitions for each stage, points for intermediate sprints on each stage, points for reaching the top of a climb first etc, and therefore lots of winners of aspects of the race besides the overall winner. The early stages are generally selected to be ideal for a sprint finishes and none of those in contention to win overall would be capable of competing in a sprint with a pure sprinter like say Cavendish, so they just stay safe in the peloton. (To be able to win overall you have to be a good climber and a pure sprinter is unlikely to be a good climber.) In the old days, a great cyclist like Eddy Merckx would have tried to win every type of stage, but it has become much more specialised these days and it is unlikely anyone would be able to do that now.
Anyway, well done, a superb achievement.