A moderate activity would be a brisk walk. Other activities include gardening, bicycling and swimming. You don't have to do 30 minutes at one time. You can break it into periods of at least 10 minutes each. This may help you get started.
Many people can start exercising without seeing a doctor first.
But if you take high-blood pressure medication, have heart disease, have had a heart attack or stroke, or have another serious health problem, you should check with your doctor before starting. Otherwise, get out and get active. Work up to a comfortable pace and schedule. It may be hard to stick with an activity, particularly if you feel pressed for time. It may help you keep going if you do an activity with a friend or family member.