This spell causes two additional arms to grow from your sides and coordinate their efforts to help you grapple another creature. These extra arms give you a +4 circumstance bonus to grapple checks you make while the spell is in effect. The arms are not coordinated enough to wield weapons, manipulate tools, or perform any action other than grappling.
If your caster level is at least 9th, you grow four additional arms, and the circumstance bonus increases to +8. These bonuses don't stack with the normal +4 bonus in grapple given to any creature with more than one pair of arms.