Primary Election vs. General Election
In Pennsylvania's Primary Elections, voters choose their party's nominees to run in the General Election by casting ballots.
Pennsylvania holds closed Primary Elections, meaning you must be a member of the party to vote for that party's candidate (for example, you could not vote in the Republican primary unless you are a registered member of the Republican Party). The candidates that receive the highest number of votes in the Primary Election will be the nominee representing their party on the General Election ballot.
Primary elections in Pennsylvania are held on the third Tuesday of May in all years except Presidential years, when it is held on the fourth Tuesday of April. General Elections are always held the first Tuesday, after the first Monday, in November.