You have been given a lot of great advice!
I have quite a few pounds to lose myself, and had not exercised in years.
I started using My Fitness Pal, which people have advised you of. I track everything I eat or drink in their immediatly after eating or drinking it.
I drink a 16 ounce glass of ice cold water before every meal.
I only drink water during the day and have a glass of milk once a day.
Fill up on veggies, and measure your portions! (Break out the kitchen scale, measuring cups, and measuring spoons!) Measuring everything is of utmost importance!
Start walking. Even if you can only do 10 or 20 slow minutes the first day. Each day you go walking, try to go a minute or two longer. Your speed will increase as well.

Keep hydrated!
Make sure you get enough potassium! I had a big scare and an ER visit due to a deficiency in potassium levels. My Fitness Pal has a break down you can look at to see the recommended daily amount for different values, as well as how many you have reached and how many you have left. This is really a valuable tool for me.
Try to reduce the sodium you take in daily.
As far as what particular diet you should follow, I suggest you talk to your doctor with your pre-diabetic condition. He or she should be able to give you some good food choice ideas.
Be prepared to cut out white carbs. If you currently eat a lot of these, be prepared for pretty intense cravings initially. When I would feel a craving come on, I would drink a glass of water and get out and walk for a few minutes. Distraction will be your best friend!!
Take the time to "search" the forum and you will learn a lot. There is a lot of support here, and I'm glad you found us! I've been here since January, and these great people are one of the main reasons I'm still motivated!
Welcome and hope I was able to help!!