Some plans you might find on these forums or in a book may help you to know where to start, but you need to adapt what you find to your own needs. Listen to your body and keep it simple.
Like mcsolar, I would note that it's not necessary to be in a gym to do cardio. If the atmosphere deters you or makes you feel uncomfortable in any way, you can always do cardio outside.
Running is a great way to lose weight. You don't need any equipment except some running shoes (but try to splurge on these, it's your only equipment!) and you can do it anywhere. I was never fond of running, despite my father being a serious runner. But, I tried it again more recently and found it to be much better than I remembered (and a very effective weight loss exercise). I was able to stick with it and enjoy it because I didn't overdo it starting out.
In the past I was trying to keep up with someone else, but this time I started slow and concentrated on consistency. I was able to run half a mile when I started, but instead of focusing on how far or fast, I just focused on doing it every day. I was able to increase mileage over time, and am now running 5 miles in addition to other cardio and lifting! But the only reason I am able to do so much now is because I built a strong base. I listened to my body and took my time. So, don't try to be a super athlete your first day out. Get rid of preconceptions of what you should be able to do, how fast you should be able to go, etc. Just go out and see what you can do. Sure, push yourself now and then, but don't over do it. If you take it slow and are able to enjoy what you are doing, you are more likely to stick with it.
Also, it helped me to set a goal
. After running a couple of weeks I decided I needed something to look towards. I signed myself up for a 5k a couple of months down the line (At active
you can search for local physical activities and events of all kinds). I told everyone I knew that I was going to run it. So, I couldn't back out.
It was great motivation to keep running, and running the race made me want to keep running. My family and friends were all cheering at the finish line, and it felt really good to accomplish a goal. It also shifted my focus to performance based goals rather than weight goals.
After the 5k, I signed myself up for a half marathon, and I'm going to run that in April. Every time I want to skip a day I think of all the people I'd have to tell if I couldn't do the half marathon. The thought of the embarrassment is enough to get me out there.
My activity of choice is running, so I am using that to explain the principles that helped me. If you don't like running you can transfer these principles to just about any other activity. I also like to climb mountains and I did the same types of things for that activity.