Giving effective written feedback to learners

I am Moreri Ramosobatha, a student lecturer at FCTVE, Botswana. I am currently doing my action research of giving effective feedback to learners , so I am asking for your cooperation on the following questions;

1. What is feedback?
2. Why is it important for facilitators to give learners feedback after every assessment?
3. What to be considered when giving learners feedback?
4. When to give feedback to learners?