The Spell Reaving Dispel acts like a Dispel magic except that you can get a maximum of +25 caster level check instead of the usual +10 (or +20 for a Greater Dispel).
If you want, on a targetted dispel or counterspell, you can opt to steal any spell you sucessfully roll a dispel check on instead of dispelling it.
If you want to identify the spell before stealing it, you need to make a Spellcraft check of 25+Spell level, else you automatically identify it after you steal it. (But if it happens to be a Geas or a Dominate person... and you didn't identify it and stole it anyway... too bad for you...).
After stealing the spell you have full control of the spell (dismissal, concentration, etc), you take it as though you were the original caster of the spell.
Spells dispelled in an area dispel, cannot be stolen.