snberk103, I don't think that this functionality is there any longer. Especially with the web version, there is no menu at the top.
In the iCloud version, there's no toolbar button for Functions. You type an '=' into the cell where you want to insert the formula, and that opens a sidebar from which you can select the desired function.
In 3.x for Mac, there
is a Function button on the toolbar. If you select a group of cells, click the Function button, and select a Function from the menu (Sum, Average, Minimum, Maximum, Count, Product), it will insert the results in the adjacent empty cell, just like AutoSum.
Alternately, you could select the cell where you desire the results, click the Function button, and select the Function from the drop-down list - Numbers will then make an educated guess as to what range of cells you'd like to have summed/averaged, etc., just like Excel.
My guess is that the developers consider this an enhancement of AutoSum, as more functions are available. However, I, too, would like a one-click solution - why not offer dedicated buttons for Sum, Average, Minimum, etc. that can be optionally added to the toolbar? I've made that, and several similar suggestions/requests to Apple (I'd also like to be able to add additional functions to the Functions drop-down, and be able to assign keyboard shortcuts...). Never hurts to add your suggestions to the pile.
