Short answers based on how Odds works today. For eligibility and shipping policy details, see the Terms of Service (including the 18+ requirement). There is no separate responsible-play page beyond the Terms and Privacy Policy.
Boxes and odds
Each box has a fixed price and a pool of items with published weights. When you open a box, the server draws one in-stock item using those weights, charges your wallet (bonus credit first, then cash), and places the win in your inventory as pending.