I was also thrown in to it in a primary school - it took a long time even to find out how the school did the most basic things - just give yourself a break and realise that you CANNOT work it all out in two seconds flat. I spent a lot of time in my server cupboard trying not to get upset as I didn't know what the heck I was doing. REMEMBER - no one else has any idea what you do so as long as you look confident, you will do OK!
As for licences - I quickly made a list of those I didn't have, submitted it to SMT and got a WRITTEN answer stating that I was not responsible for those that they couldn't find. I quietly stated that, as licences are my responsibility, I would remove unlicensed software from the network - I gave them a grace period of 2 months to sort it out. They did.
Initially you just need to know how to create users, clear printer problems and the like - this will keep you going as you slowly get to grips with what goes where and why. (although it has to be said that 4 years on, some things are still not as I would like them, but we are getting there!!)
Good luck, and please pm me if I can help in any way (back at work next week)