If you want to start working out, but are a beginner, remember not to do too much too fast to prevent injury.
Light Weights
Start with 3lbs and move on to 6lbs when you feel you are ready.
Run/Walk
Run until you are getting out of breath and then walk, then run again when you feel up to it. Repeat for a mile or 2.
Bike
Whether this is at the gym or outside on your bike, it is a great option for you to start getting in some cardio.
Hiking
Finding a trail and getting into nature can be a great workout, but is also great for you mentally.
Swimming
If you have a pool at your gym, don't let it intimidate you. Grab a kickboard and just kick the length instead of feeling like you have to have perfect swimming skills.
Plank
Planking is a good whole body workout and a great place to start.