I'm looking for a short commonly used phrase with meaning "very simple, straightforward, without unnecessary details, with basic terminology" in context of explanation of some idea or phenomena. It may be an idiom or a catch phrase, the main requirement is being widely used and understood by everyone. For example, in Russian there is an idiom "объяснить на пальцах" (literally "explain on/with fingers"), it is used to explain complex subjects with simple terms and examples ("fingers").

My first idea was "for dummies" from the book series title, but as far as I know this phrase usually used for new topics, and it is not really used for rehearsal education. Another idea came from "Simple English Wikipedia", but I'm not sure if phrase "explain in simple English" is really widespread.