How do National Conventions select a candidate?

The political parties in the United Sates choose their candidates through a Primary voting system. However, the voters do not select the candidates directly, but they pick delegates from their states, who will go to the National Convention in order to Nominate their party candidate. The National conventions include delegates, and also “super delegates,” who has not been selected by voters, but are powerful people such as governors, ex-presidents, and such. They have been devoted to the party for a long time and because of that have been awarded a final vote in the National Conventions.