One of the best ways of exercising aerobically is walking. Much has been said about 10,000 steps a day. Actually 12,000-14,000 is better but I lost weight regularly when I watched my diet and got 7000 per day which doubled my total of usual steps.
The pedometer I recommend is one made by Omron. Called the pocket pedometer, it can be carried in a purse, backpack or pocket to record your activity. It can be but does not have to be attached to your belt. I have one and got it from Amazon. I have been pleased as it has a clock, counter, 7 day history, and lets me know the time spent time of day and steps walked.