Refers to the manner or method of using something; often implies that the outcome depends on how it is used.
この道具は使いようによってはとても便利だ。
Depending on how you use it, this tool can be very useful.
Money can change your life depending on how you use it.
Kanji spelling using 様; less common but still seen.
Compound of 使い (the continuative form of 使う, 'to use') and 様 (よう, 'way, manner').