Thank you, as ever, for your excellent help on these pages. However, I should say that "Its use is simple" is not very good English, whereas "It is simple to use" is much more natural. I think there may be a thin line here between 'idiomatic' and 'accurate to the language to which you're translating'. Thank you again, with gratitude and respect.
There are always various ways to say things in every language and you are learning various ways of saying that "it is simple to use". You are learning the noun "une utilisation", which translates to "use" or "utilization", as nouns as well.
You may find "c'est simple à utiliser" or "il/elle est simple à utiliser" in this course, and it will then be the right time to translate it to "it is simple to use". Eventually, you will know two French ways of saying this.