To be usable or serviceable; to function well enough to be useful (can refer to tools, functions, or people).
古いパソコンだけど、まだ普通に使えるよ。
It's an old PC, but it can still be used normally.
彼はどんな仕事でもそつなくこなせる、使える社員だ。
He's a reliable employee who can handle any task — a useful person to have.
このアプリは古いOSでも使えるように設計されている。
This app is designed to work even on older operating systems.