Hi I am new too. I also sit allll day at work. This makes getting those energy levels up difficult but for the past few months I have been increasingly exercising more and cutting my calories (I do slip here and there!). One thing I read about burning a few more calories at work and building a little muscle - is to not assist yourself when you're getting out of your desk. Rather than push off from the desk to move your chair away before you get up, use your legs to push the chair away. Then, when it's time to get out of the chair DO NOT balance your arms on the arms of the chair or use them in anyway, instead use all your leg and core strength to get up out of the chair. You're forcing your muscles to be at work when you're at work! We grow so used to assisting ourselves when getting up by using our arms which totally puts a damper on our core and leg muscles. Seriously, try it - just that little effort can make a difference if you do it every time. And do it when you sit down - don't use ANY arms when sitting down in your chair. So you might make a few grunts or lose your balance at first - you'll get better. Thats a good way to start. If it's been a long time or perhaps never since you've worked out - DEFINITELY start w/walking. Walking alone burns 80 cal/hour (if I recall correctly). but the biggest thing I keep hearing is creating a calorie deficit. Most of your fat loss is going to be directly correlated to your diet. I eat 5-6 small meals a day. Stick my carbs in mostly in the morning - stick to good carbs like whole grain bread and good veggies, between b-fast and lunch I do a yogurt or piece of fruit and have a good salad with little fat and lots of protein for lunch, another snack a few hours later such as some beef jerky or something else high in protien, and then a good low carb - low fat dinner if I find time. It takes dicipline but eating smaller more frequent and HEALTHY meals is the way to go- it speeds your metabolism and keeps your body working - and guess what?!?!! it works. I've lost almost 20 lbs.
Good luck. I'm right there with ya as I feel like i'm still a beginner here.