To turn on a switch (power or function) for a device; figuratively, to switch one's mindset or focus on.
部屋の電気のスイッチを入れて明るくした。
I turned on the light switch in the room to make it bright.
会議が始まる前にパソコンの電源スイッチを入れておいてください。
Please turn on your computer's power switch before the meeting starts.
大事なプレゼンの前に気持ちにスイッチを入れて緊張を集中力に変えた。
Before the important presentation, I flipped the mental switch and turned my nerves into focus.
機械はスイッチを入れればすぐに動き出す。
The machine will start moving as soon as you switch it on.