Automation testing process in agile sprints

What is the best process to follow for Automation testing(selenium) in Agile sprints?

1. In agile sprints, is it a good idea to implement automation tests with out development task is completed ?
2. In agile do we have to implement automation tests parallely with development?
3. Is it required to do manual testing in agile sprints? if yes when ?
4. In agile sprints when/where manual testing come into picture?
5. When to start writing/implement Automation tests and when to start manual testing in agile sprints?

Please help me with these queries. Please suggest the best process to follow for Automation testing in Agile sprints.