you cant model as such in poser, but can make your own characters with morphs etc, if you want to make your own models from scratch you need a modeler. Modelers vary a lot in both price and functions, some are easy to learn some arn't lol. Once you have the basic skills of modeling  they will stay with you in any modeler, try the free ones first then if you want to!! get the demos of the high end one and see if you like em, does depend on what your plans are if you are just doing it for fun or hoping to make a living, could take a while to recoup the cost of an high end app but we all chuck buckets of cash at a hobby lol