Besides swinging your sword or casting spells, you can also use various magical devices found in the world. There are two main types of magical devices:
Scrolls are spells that have been stored on parchment for later use. These are one-time use items and the scroll is consumed after the spell is cast. Characters with the Scribe feat can create new scrolls with spells they have memorized.
As a general rule, a player may use a scroll spell that exists in their class's spell list with no penalties, provided they actually meet the requirements for casting the spell. Players may only use scrolls with spells from their own classes' spell list, with a few exceptions.
Thieves and Bards with the Use Magic Device feat, or Cyphers with Enhance Scroll, may use any scroll as long as they have a casting stat (intelligence, charisma, wisdom) that meets the requirements for the spell (stat - 10 > spell level).
Wands and enchants are magical items that cast spells. Unlike scrolls, they tend to have multiple uses, or charges. These items will simply work for the user, though the efficacy (clevel) is determined by the user's character level.
The Stat Mod used is your highest among CHA, WIS, or INT
Caster Level = character level
Eldritch Melding feat gains +3 clevel on device usage
No Success Check
Caster Level = Spellcraft Skill (max 50)
No Success Check
Caster Level = Spellcraft + (3 from enhance scroll) (max 53)
Insightful Scroll Retention Chance = (20 + spellcraft / 2) percent
Caster Level = Thief/Bard Level + Prestige OR Spellcraft (whichever is higher) (max 50)