The role of a campaign manager is to

select a candidate to run for office.
contact the media on a daily basis.
donate money to buy campaign materials.
oversee a campaign organization.

The role of campaign manager is to oversee a campaign organization. He is responsible for coordinating the operations and activities of the campaign on day to day basis, and the activities that indirectly or directly support the campaign. He manages the activities and makes the campaign effective. His responsibilities include management of staff, coordination with the candidates, looking after campaign budget.