You're the only one that can answer either of those questions. you just have to pickup some weights, and start moving them, to see if they're too heavy, too light, or just right.
don't worry if you're curling 10lbs and the woman next to you is curling 25lbs. its not about her...or how you compare to her...its about what you can do now, and what you're working towards.
you'll know you're working the muscles because you'll feel it. the slight burning at the end of the set...the slight stiffness the next day.