Full Control
Freely, At Will
noun, な adjective, の adjective
When you're all by yourself and only your self exists, you probably have full control. You can do whatever you want freely and at will.
自在 is commonly used with the particle に to form the adverb 自在に. This describes how someone can handle something effortlessly, as if they have full control over it.
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.