The goal in Oust is to completely clear the board of enemy stones, to oust your opponent - a paradox since the board is empty to begin with. Your opponent has to add at least one stone before you can capture all of his stones.
Non-capturing placements: A non-capturing placement either forms no connections (adjacencies) with any stones, or forms one or more connections only with enemy stones. A noncapturing placement does not form any connections with stones of its own color.
Capturing placements: When you place a stone which forms one or more connections with your own groups, you create a new, larger group of your own stones. You can only make such a placement if said new group will have one or more connections with enemy groups upon its creation and if all said enemy groups are smaller than said new group. Upon making such a placement, all said enemy groups are removed from the board.
Multiple placements per turn: After capturing one or more enemy groups and while it is still your turn, you must continue to add stones until you make a non-capturing placement, at which time your turn is concluded.
Pie rule: on his first turn only, the second player may choose to play as the first player instead of making a regular move.