A spell scroll is a magic item that holds a written form of a spell, that, if read properly, by the appropriate type of spell caster, can be cast exactly like the spell as if you prepared the spell. 

The scroll itself is the only spell component necessary during casting. Once cast, the writing (for that individual spell only) will fade from the scroll material, gone forever. While casting a spell from a spell scroll, you are immobile as if casting an actual spell. See also spell disruption below.

The type of scroll, if unknown, can be randomly determined:

Cleric Scrolls. The contents can be discerned by any cleric that scans the scroll as a complex activity. After this, the cleric can cast any spell contained on the scroll. Unless described differently, other classes cannot read cleric scrolls. A read magic spell cast by a non-cleric will give the caster knowledge of the contents of the scroll but will not allow it's use. Shaman (that have the ability to read - most do not!) can use cleric scrolls.

Druid Scrolls. The contents can be discerned by any druid that scans the scroll as a complex activity. After this, the druid can cast any spell contained on the scroll. A read magic spell cast by a non-druid will give the caster knowledge of the contents of the scroll but will not allow it's use.

Illusionist Scrolls. The contents can be discerned by any illusionist that scans the scroll as a complex activity. After this, the illusionist can cast any spell contained on the scroll. A read magic spell cast by a non-illusionist will not allow the caster to discern the scroll's contents. However, a comprehend languages spell cast by a non-illusionist will give the caster knowledge of the contents of the scroll but will not allow it's use.

Magic-user Scrolls. The contents of the scroll cannot be determined unless a read magic spell is used. Once cast, the caster can scan the scroll as a complex activity. After this, if the caster is a magic-user, the caster can cast any spell contained on the scroll.

Educated Checks. [complex] A magic-user can attempt a DC 15 educated check to determine the class type of any scroll by scanning it.

Caster Level. Each scroll will have spells written at a particular caster level. When cast, the spell operates at the level it was written, not the caster level of the one doing the reading.

If unknown, determine the caster by finding the highest level spell written on that scroll—the caster level will be the lowest level required to cast the spell plus one (minimum 7th level). 

Example. A magic-user scroll is found containing the following spells: magic missile, fireball, and ice storm. The caster level for all of the spells will be 8th level (ice storm is the highest level spell and requires a minimum caster level of 7th; Add one and caster level is 8th).

CASTING SPELLS FROM SCROLLS

Spell Scroll Invocation. [spells; invocation] (major, casting time of the written spell +2 segments if the scroll is not in hand) The caster must have the scroll in hand in order to cast a spell from it. If the scroll is not in hand, the caster is allowed to get the scroll from a readied spot (typically a readied scroll tube) which adds 2 segments to the casting time of the scroll. The caster then casts the spell from the scroll. When cast, the spell disappears from the scroll and if there are no other spells contained on the scroll, the scroll will crumble into ash. Stowing a scroll into an open/readied scroll tube is a major action. Accessing a scroll in a non-readied scroll tube is delaying activity (major action; so the spell on the scroll cannot be cast until the next round).

Spell Disruption. A caster reading a spell from a scroll can have the spell disrupted, however, if this occurs, the spell is not lost even though the attempt to invoke it fails. The spell is still contained on the scroll (assuming the scroll is undamaged) and can be cast at a later time.

The Spell is High Level than the Caster. If the spell being cast from a scroll is higher level than the caster (i.e. the caster cannot access that level of spells in the spell list), there is a chance of spell failure.

SPELL FAILURE

Even if the spell is read without interruption, if the caster level of the spell is higher than the caster level of the one reading the spell, there will be a chance of spell failure. 

The chance is equal to 5% per level of difference in caster level. 

Important Note: In this case, the caster level of the spell contained on the scroll is the MINIMUM caster level required to cast the spell in question—not the caster level at which the spell is written.

Thus, a 2nd level magic-user, attempting to cast an ice storm spell from the scroll in the example above will have a 25% chance of spell failure ([7th-2nd]=5 * 5%=25% chance). If a spell failure is indicated, use the provided table.

Charges. None (i.e. not applicable). Once cast, the writing (for that individual spell only) will fade from the scroll material, gone forever. All other spells written on the scroll and uncast, remain.