To throw into (to toss something into a container, place, or space).
ゴミ箱に紙くずを投げ込む。
I throw the scraps of paper into the trash can.
彼は封筒に書類を投げ込んで去った。
He tossed the documents into the envelope and left.
子どもが川に石を投げ込んだ。
The child threw a stone into the river.
郵便受けにチラシを投げ込むのはやめてください。
Please stop stuffing flyers into the mailbox.