Each pack contains 2 Jumpstart Booster packs 

There are ten themes in The Brothers' War Jumpstart Boosters, two versions within each color theme:

White: Infantry
Blue: Powerstones
Black: Unearth
Red: Welded
Green: Titanic
Each The Brothers' War Jumpstart Booster contains a theme description insert plus 20 total Magic cards:

1 Rare card—one random rare or mythic rare from The Brothers' War within the theme's color, or a colorless rare
1 Rare card that is unique to Jumpstart Boosters
2 Traditional foil lands
6 Non-foil lands
There are five new rares among The Brothers' War Jumpstart Boosters, one in each booster that matches that booster's theme