Korean double cleansing - is it necessary and how to do it right?

I keep hearing about the Korean double cleansing method but I am not sure if it is necessary for my skin. I wear SPF daily and light makeup. Is double cleansing really necessary or just a trend? If I should do it, what is the correct technique? I am confused about oil cleansers - will they break me out? What are the best Korean oil cleansers for someone with oily, acne-prone skin? And should the second cleanser be foam, gel, or cream? I want to cleanse thoroughly but not strip my skin.