Are breastshields necessary? How do we use them?

Breast shields are worn in bras to aid breastfeeding when you have flat, inverted or sore nipples. You slot them into your bra, that's all. You can also use them to collect your milk instead of using a breast pad. I have breast shields but don't use them. It's not necessary for me as I'm home most of the time and don't have problems breast feeding. https://en.wikipedia.org/wiki/Breast_shell