Most gyms you can request a trainer if you are just starting out, but if you want to start out without a trainer, make sure you have researched some of the exercises you want to do to reach your goal either with free or weight machines.
The best way to start is to figure out how many days you can workout,, usually three days a week with a day rest in between the next exercise day. Next would be to figure out how much weight is a good to start with out experiment with weight to see how much you can lift. I would recommend 8 to 10 reps 3 sets with a rest in between the next set keep but your heart rate up, when you feel comfortable on you 3rd set with lifting more reps you are ready to increase weight by at least 5 pounds. Kept this routine up for 3 to 4 months. Two days a week should be upper body , the third day legs. Do arms and shoulders day one, legs day two, chest and back day three. This exercise is for bodybuilding and tone, strength you need more weight less reps but still do 3 sets. When you get used to working out try to do two different exercises per muscle. The biggest obstacle a lot of people face is not sticking with exercising so keep on keeping on no matter how hard or bored you get with it, you will be very happy with the results.