Ooh GreenMouse - another convert 
Crowler - no
Your outgoing transactions are never reflected in your Available to Budget balance unless you have allocated money to the categories they sit in. The Available to Balance budget is purely the amount of money that is in your account, that isn't already allocated.
Any incoming scheduled transactions will be reflected in your ATB, because it's income that you allocate to spending.
If you get paid £1000 and have budgeted £1000 to rent, then your ATB will be £0.
If you then spend £1000 on chocolate instead, your ATB will still be £0, but you will have underspent your rent budget by £1000 and overspent your chocolate budget by £1000.
I know it seems a bit confusing, but it's because most budgeting softwares are actually 'spending trackers' - you project how much you'll get each month. You project what you'll spend it on. Then you look to see if you actually did what you said you'd do.
YNAB is the other way round. Spending is the very last bit of the equation. In YNAB you get the money, give it a job, then spend according to your budget. If you want to spend money in a category that you haven't allocated money to, then you either shift money from one category to the other, or you live with the fact that you've overspent.
It does make sense, once you've got it, but it turns budgeting completely on its head.
The best thing you can do is to make a new local budget and play! See what happens when you put £500 into the account. See what happens when you spend in a category that you haven't allocated money to. Play with how to increase the balance in a category, or to swap categories. Etc, etc.