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.
かいほうする
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.
夜はオフィスをバーとして開放しています。
We open our office up into a bar at night.
夏はこのプールも公共に開放されます。
In summer, this pool is also open to the public.
月に一回、美術館が市民に無料開放されます。
Once a month, the museum is open to citizens for free.