I started out last year on my weight loss journey.
I was 115kgs.
Exercise wise I started out on the treadmill, when I first started it took me around 1 hour to walk 2km.
I'm now 65kgs and jog 10km every day and do a 20km jog 3 times a week.
For me it was just pushing myself that little bit further every time I walked (I did start out just walking)
Also just when ever I felt my body could handle it i was doing bursts of jogging, each time just trying to make the bursts longer.
Each time I started on the treadmill I would have a goal, it was always to beat either the time or distance I did the day before.
When I confident enough I would set out jogging routs around my area for a certain distance and try and beat the time it took me previously.
I did also do other forms of exercise whilst loosing weight.
Light weights for my upper body, squats, the Wii-Fit.
Just remember to eat enough food to account for the exercise you do, you do not want to burn yourself out!
That is very important.
A high carb meal (I prefer brown carbs) about 2 hours before a jog is an excellent way to push yourself further and give your body enough fuel to burn.