Primaries use secret ballots, similar to those in general elections.
Primary voters choose a slate of delegates who are affiliated with a particular candidate.
In most states, those delegates sign a pledge to vote at the state convention for the candidate they represent. Each state regulates its primaries or caucuses differently. The Constitution contains no guidelines for the nomination process, so it's mostly regulated by the two major parties, which have adjusted the process over the years to both suit their interests and respond to public demands. In Ohio, the presidential and vice presidential nominees of the major political parties are not nominated through primary elections, but are selected by delegates at each party's national convention. The number of delegates and alternates to be sent to a convention is determined by the national party committee's written rules governing the primary process in each state.