The easiest way is to go to your first month’s budget, change the “Adjust Modifies” setting (in G14 by default, I think) to “Savings”, then go through and enter the amounts you want to allocate in each category (in the green boxes). Once you are done, be sure to run the “Update Savings Budget” function. There’s some more detail on the Savings Budget page.
Those amounts will be reflected in the second column. If you look at the top, next to “Expense,” it will tell you the total amount you have allocated. You can compare that to your start of the month bank balance to see how much is left.