The ability that governs bonus spells depends on what type of spellcaster your character is: Intelligence for wizards; Wisdom for clerics, druids, and rangers; and Charisma for bards, paladins, and sorcerers. In addition to having a high ability score, a spellcaster must be of a high enough class level to be able to cast spells of a given spell level. See the class descriptions in Classes for details.
If your class level is only high enough to cast 1st level spells, then that is the only level you get bonus spell slots for. You wouldn't get any of the bonus spell slots of 2nd level or higher until your class level is high enough to cast spells of that level.