A couple things you need to do.
Hit the gym or the weights in your apartment/house and start light.
Once comfortable, move up to higher weights gradually!
Eat quality proteins and make sure you take a pre-workout and post-workout drink for muscle building and recovery.
Higher reps with light weights are for definition and fat burning.
Medium heavy weights doing 8-12 reps are where most people build more muscle and heavy weights with low repsr build more strength.
Be patient, as everyone progresses at a different rate.
Buy a men's fitness magazine to get some more ideas and perhaps some inspiration
I put Arnold Swatchenager's poster up in my basement (when he had won the Mr. Olympia title in 1980) and this made a big difference for me.
Visualization, ample rest, optimized nutrition, staying hydrated, a workout buddy, perseverance and commitment will all help reach your goals and make you feel better.
You can do it!
I'm 62 and I workout 10-15 hours a week. Treadmill, elliptical machine,
free weights, stationary bike, stair climber, multistation weight machine,
I'm in better shape than most people I know, even people in their 20's.
But the most important part is that I'm healthy and feel great!