Sorcery is intended to be played in whatever way you and your friends find most enjoyable! If you're attending a tournament, it's wise to be aware of the rules that will apply, ensuring that everyone attending the event understands how it will work. Tournament organizers are empowered to modify the rules to maximize the fun of the players in their community, including banning or modifying cards, modifying the setup rules to provide some compensation for going second, etc. For example, one such setup rule is that after mulligans, the second player may look at the top card of their spellbook or the top card of their atlas, and then may put that card on the bottom. Please check with the tournament organizer of any events you attend to ensure you understand the rules that will be in effect, and most importantly, have fun!