I would start with a full body workout 2-3 times per week. Begin with machines for you first lifting experience, as this will get you're muscles used to lifting weights, as well as help to prevent injury. Do 3 sets of 10-15 reps per exercise. I'm not sure what type of machines you have at your gym, but if you can find machines that fit the general description of:
Chest press (either lying down or sitting)
Rowing machine (close grip attachment if possible, probably looks something like a V shape)
Shoulder press (alternate between inside and outside grips to see which is more comfortable, you'll probably find the inside to be easier)
Leg Curl (sitting, standing, or lying face down, it varies from gym to gym)
1-3 ab exercises depending upon fitness level, start with 3 sets of say 10 reps, then work your way up from there, you may even be able to do more now, if so, start with say 3 sets of 15 reps (see exercise guide on main shapefit website for guide of abs. Try a couple the first week, and then pick your favorites for the rest of the time)
Do this workout, or some similar variation, for the next 6-8 weeks, then come back and someone will be able to recommend another workout for you.
Feel free to ask as many follow up questions as you can think of. The more educated you are before you start lifting the better. And always remember to air on the side of caution. There's a fine line between pushing your body to its limits to gain muscle and doing something that will get you hurt.