Il n’en fait qu’à son idée.
eel nah fay kah saw nee-DAY. Click below to hear this!
He does just as he pleases.
Okay, okay, it’s a loose translation. Really: He does only according to his idea. Not especially good English, but at least it makes sense.
So une idée in French is more than a brainstorm. It’s a thought, a plan, an impulse, a conception, an understanding. Remember that ne…que means only, no more than. In this sentence, à means in accordance with, according to. And don’t worry about what the word en is doing in there. Sometimes a word doesn’t correspond precisely to anything when you are translating…it just needs to be there!