Hi there - and as veryone else has said, "Welcome aboard".
A few points that may be of use/interest (feel free to ignore - see rule "1")
1) Rule "1" - it is your (and your friends) game. You may run into some oiks who try to tell you you are playing badly/wrongly/whatever. Ignore them - if you are having fun, then you are doing it "right" (in so far as that means anything). Hopefully you won't run into any idiots like that, but they are around
To expand your game, there are a couple of things I can recommend
2) Have a look on line - there are LOTS of things you can (quite legally) lift from web sites and use. Paizo here has some add on adventures specifically for the Beginners Box; Likewise, there is an additional PDF you can get designed to make moving to the "full" game much easier. Have a look, and don't be afraid to steal ideas
3) Using pre-made adventures. Thoughts on this vary, as many people like to create their own adventures, but I think when you are just starting out, having a helping hand with a pre-designed adventure is a really good idea. There are some designed specifically for the beginners box as complete adventures. I am cursed with a bad memory though, so can't remember the names of them. I believe they had quite reasonable reviews, though, so may be worth looking up
4) If you want to spend some money, some of the better options include:-
a) The Bestiary 1 - a whole lot of new monsters. If there are sections on the descriptions or stats you don't recognise, ignore em, and just use what you recognise
b) The GameMasters Guide is also a good book if you are just starting out. It gives you a good grounding on running adventures, how to handle problem players, etc etc. Pretty good book in my opinion
c) The Core Rule Book ("CRB") - bit odd listing this one last, as it is truly the core of the system. The reason I listed it last is that it is chock full of rules... The others have bad guys you can pick and choose from, or good generic advice on what to do. The rule book has a lot of rules and can be overwhelming. Very very good book, aned essential at some point, but read the PDF I mentioned at the top first if I were you.
5) Have fun - never get so bogged down in rules that you spend 30 mins trying to work out what the book says - take a punt, guess at how hard it should be, and make the player roll for it ("OK - you are wearing a blindfold, on the back of a dragon, and you want to jump off just as it passes over the mill pond (which you can't see), stealing the bad guy's dagger as you go, making a perfect swan dive while singing "All Hail Desna". "sigh*. OK - lets start with a perception roll, DC 35 or so and work from there..."). Look up the rules AFTER the game - try not to use too much time in game.
Bahh - I could go on and on, boring you to tears. I'll end with just remember it is a game, and it should be played as such, not a competition. As GM, any time you want to kill the players, you can. Your "job" (apart from having fun) is to to give the players a chance to kill themselves ;-)
Cheers
Aiddar