Hi Cara!
I'm fairly new at this too, and have had the same thought processes as you. I've only just joined 3FC but I've been lurking for a little while, and the support that I've seen dished out on here is amazing and that's what made me join!
There's lots of calculators out there that you can google which will tell you how many calories you need to maintain and to lose weight. It is different for everyone, though, so don't be disheartened if it takes you a while to find the right calorie allowance for you. Just keep playing around until you feel it's a level you can sustain happily and the weight is still coming off.
I'm in a similar situation to you, but a bit heavier - 196lbs at 5 foot 1, and though I've lost a few pounds already like you I really just want to keep the scale going down.
In my opinion, the great thing about calorie counting (other than it being free!) is that there's so much information to be had on the internet. My starting advice is do some research, plan some meals or some days, and get going. It's cheesy, but like they say a journey of 1000 miles begins with a single step!
Keep posting, and keep positive, and good luck.
X