To Open Something Up
To Throw Something Open, To Open Something To The Public
する verb, transitive verb
When you open then release, say, a door, you're opening it up for everyone to come in. That's why it means to open something up or to throw something open.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
このそうこをひなん所として開放することになりました。
They decided to open this warehouse as a refuge.
このプールは、夏の間、一ぱんに開放されます。
This pool is open to the public in the summer.
あるゲームにアクセスするために、ポートを開放する方法が知りたいんだ。
I want to know how to open ports to give access to this one game.