SECTION PREVIEW:

Walking
Don't worry about how far, focus on enjoying yourself, creating challenge, and building stamina and endurance.

Elliptical trainer
Excellent full-body cardio, just make sure to raise the resistance setting high enough to engage your whole body; low-impact.

Swimming
Extremely low impact, perfect for individuals who prefer low-risk, full body movement.

Bicycling
Also generally low impact; great for elevating heart rate. Set resistance appropriately for stationary bikes. 

High Intensity Interval Training (HIIT)
Good for elevating heart rate. Can increase risk of developing task aversion. 

Running / jogging
Great for functional training. Always practice safe and effective technique.

Regardless of which exercise  is chosen, always practice good form and try not to overdo it. With time and repetition intensity may be increased.

Always remember to REST as needed and to be done when you're done.