To put effort or strength into something; to concentrate on or exert oneself for a task; to apply force or emphasize.
試験に向けて今は勉強に力を入れている。
I'm putting a lot of effort into studying for the exam now.
このプロジェクトには営業部全員で力を入れる必要がある。
The whole sales department needs to put effort into this project.
ねじを締めるときは、最後に少し力を入れてください。
When tightening the screw, apply a little extra force at the end.
彼は発言の最後に声に力を入えて、自分の意見を強調した。
At the end of his speech he put emphasis into his voice to stress his opinion.