Each party pack contains 5 fun games from a mix of drawing games, writing games, trivia games, hidden identity games, etc.
If you want kids to play too, some of the games in the later Party Packs have a kid safe mode, to remove any risqué content.
Only the host needs to purchase the game. Although the game can run on many platforms, for video streaming I think it’s easiest if the host also has a laptop to run Jackbox and zoom (etc.) on. The host then shares their Jackbox screen to the others on the video call. Everyone (including the host) plays along on a browser on their own device, (phone, tablet, laptop, etc.)
The Jackbox Party Packs are also on sale at similar prices at other game sites, e.g Steam, Epic Games, etc. Check them too if you have a preference.