You could go for a walk almost every day but brisk walking is generally recommended anywhere from 2-6 times a week, depending on your goal. You can walk for a period of 10 to even 60 minutes each time or break it up in the day to achieve that figure.
Although brisk walking would mean different paces for different people, depending on their age, level of fitness and their health conditions, one way to quantify it technically is to walk with your heart rate showing a reading of between 65-85% of your maximum heart rate. (To calculate your maximum heart rate or max HR: minus your age from 220 to get the your theoretical max HR).
Very fit men should be able to cover a distance of 6-7 kilometres walking for an hour that is about 120 steps a minute. For women make that approximately 140 steps walking at the speed of 6-7 km/hour.
You have to remember that you need to build up your pace over a period of time, to avoid injury and bringing on adverse health reactions. Give yourself a goal to work towards and try and achieve it within a specified period but take note of the difficulties you are facing. Maybe you could start off by walking for 10-20 minutes to build up your stamina and then work towards attempting to finish 6 km in an hour, in about 1-3 months . Then within the next month, work yourself to TRY and do another 1/2 km. One tip to help you achieve this is to walk with a streamlined body i.e. arms close to your body, preferably bent at the elbows (at right angles) and move them forward and back to help you gain momentum in your stride.
Remember, do not push your self too hard and the benefits will be yours.