活学活用

to creatively combine learning with usage / to learn and apply pragmatically

to live / alive / living / work / workmanship

to learn / to study / to imitate / science / -ology

to apply (knowledge etc) creatively and flexibly / to use a word flexibly (e.g. a noun as an adjective)

to use / to employ / to have to / to eat or drink / expense or outlay / usefulness / hence / therefore