Project implementation refers to transforming a proposed project into reality through putting activities, resources, and management structures into action. It involves two main phases - project activation, which makes arrangements to start the project, and project operation, which practically manages the project to transform inputs into outputs. Implementation can use top-down, bottom-up, or collaborative approaches. A project implementation plan details the schedule, staffing, finances, reporting, sustainability measures, time controls, and supervision needed. Key factors for success include strong political commitment, careful preparation and management, and stakeholder involvement, while common challenges are financial, management, and technical problems.