Freely
At Will, Flexible, Adjustable
noun, な adjective, の adjective
When you can exist all by yourself, then you can do things freely as you please.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
ヴァンパイアは人の心を自在にコントロールすることができる。
Vampires can control the human mind at will.
彼女はスマホを、まるで体の一部のように自由自在に使いこなします。
She uses her smartphone as freely as if it were a part of her body.
その歌手は、パワフルな高音からソフトな低音まで、様々な歌声を自在にあやつることができます。
That singer has the ability to effortlessly manipulate various vocal tones, ranging from powerful high notes to soft low notes.