100+ pounds to lose

You can do it. I've lost 150 pounds in under a year. The best advice I got was just take it one day at a time.

I was too afraid to join a gym at the start, I was afraid of how others would perceive me. So I found a walking route of four miles (2 miles there and 2 miles back) and did that every day religiously. But really, diet is the most important thing you can do to lose weight. I'm now at a gym and I totally do not regret the new found stamina doing my 4 mile walk a day got me. So I still recommend it, it's hard at first but soon you won't even feel it.

I also counted my calories. I found out what my BMR is and TDEE, it's much the same thing which MyFitnessPal uses when you join and put in your age, weight etc. Generally I ate around 1500 calories a day. Being so big needs a lot of calories to maintain such a weight, so when I counted my calories a lot of weight came off fast. It gave me the encouragement I needed, because before when I had "tried" to diet, I never saw results right away and that made me give up.

TLDR: I did one simple, low impact exercise every day, and I cut my calories quite a bit.