One way of thinking of the Ribbon is like a set of graphical menus. The tabs attached to each of the Ribbons in Excel are like the menu titles and the contents of each menu is spread out horizontally and represented almost exclusively through icons. The drop-down selector arrows next to buttons lead to ‘sub-menus' with more options and the group arrow - in the bottom right-hand corner of some sections of a Ribbon - leads to more detailed dialogs.
The difficulty of relearning where all the common functions are among the Ribbons depends on what you typically use Excel for. For general users, most functions will be in the Home Ribbon and you can get quite a long way without switching between them. For others, who regularly use more of Excel's facilities, flicking between Ribbons will initially seem annoying, but in most cases, once you start to remember the locations of the commands you use, they nearly always take fewer mouse-clicks to get to.
Running briefly through the Home Ribbon, you have clipboard functions on the extreme left: cut, paste, copy and the Format Painter - the Using Templates tutorial includes coverage of the Format Painter. Next there are font functions, for changing the look of text within a worksheet, and alignment functions, for choosing where it's placed in a cell.
Being based on numbers, there are also quick ways of getting at numerical formats, in the Number group, and then a big group for Styles, where you can quickly set up an overall look for the cells in your worksheet or table. This is also where conditional formatting and tables can be created - there's more coverage of this in the Quick Graphs tutorial.
Cells have their own group, so inserting and deleting rows and columns is now a single-button click. The Format button within this group gives you a menu with a quick way to adjust column widths to the widest entry, which is a big time saver. The Editing group includes find, sort and summation functions, among others.
As with the Word Ribbon, some Ribbon groups in Excel only appear when you're working with particular objects, such as tables or graphs. Some functions, like recording Macros, are still rather too well hidden, but most people find the revamp of Excel's functions to be an improvement, once they've worked with the program for a couple of weeks.