Reference:
http://blog.scrumstudy.com/exploring-the-implement-phase-of-a-scrum-project/

Affinity estimation is a technique used to quickly estimate a large number of User Stories. Using sticky notes or index cards or tape, the team places User Storied on a wall or other surface, in order from small to large. For this, each team member begins with a subset or User Stories from the overall Prioritized Product Backlog to place by relative size. This initial placement is done in silence. Once everyone has placed their User Stories on the wall, the team reviews all the placements and may move User Stories around as appropriate. The second part of the exercise involves discussion. Finally, the Product Owner will indicate some sizing categories on the wall. These categories can be small, medium or large, or they may be numbered using story point values to indicate relative size. The team will then move User Stories into these categories as the final step in the process. Some key benefits of this approach are that the process is very transparent, visible to everyone, and is easy to conduct.

Explanation/Reference: http://blog.scrumstudy.com/selecting-appropriate-scrum-masters-and-identifying-relevant- stakeholders/

Quality control refers to the execution of the planned quality activities by the Scrum Team in the process of creating deliverables that are potentially shippable. It also includes learning from each set of completed activities in order to achieve continuous improvement. Within the cross-functional team, it is important to have the skills necessary to perform quality control activities. During the Sprint Retrospect Meeting, team members discuss lessons learned. These lessons act as inputs into continuous improvement and contribute to the improvement of ongoing quality control.
Quality is required not only in products, but also in processes. Quality assurance refers to the evaluation of processes and standards that govern quality management in a project to ensure that they continue to be relevant. Quality assurance activities are carried out as part of the work. In fact, quality assurance is a significant factor of the definition of Done. The deliverable isn't complete if appropriate quality assurance has not been conducted. Often, quality assurance is demonstrated during the Sprint Review Meeting.
Reference: http://blog.scrumstudy.com/quality-control-and-quality-assurance-in-scrum/