What are characteristics of vice president?

Vice presidents will become president if anything happens to the president (sometime described as a heartbeat away from the presidency.) So, they need all the qualifications of a president, at least in theory. In practice, until Eisenhower made a special point to give VP Nixon responsibility, vice-presidents were essentially useless unless the president died. The only official duty of the VP is to preside over Senate debate and to vote if there is a tie vote- not very likely to be important, since the Senate can delay a vote if the VP could really make a difference.
The VP candidate was often chosen to balance off the presidential candidate in hopes of picking up votes from people not likely to vote for the presidential candidate. For example, Lyndon Johnson, a powerful Texas Senator was added to the Kennedy ticket. Andrew Johnson, from Tennessee, once a slave state, was added to the Lincoln ticket.