godan verb (-su), transitive verb
master; handle skillfully; make full use of
Implies not just using something, but using it with full proficiency, having mastered its functions or nuances. Often used for tools, software, languages, or skills.
彼は新しいソフトをすぐに使いこなせるようになった。
He quickly became able to master the new software.
この包
Even professional chefs find it difficult to handle this knife skillfully.
英語を使いこなすには、たくさんの練習が必要だ。
To acquire a command of English, a lot of practice is necessary.