Your request is incredibly broad. Generally, you don't animate Excel graphs on After Effects. You animate graphs, period. Excel is long out if the loop at this stage. Sure you can import the data, but its not inside excel its inside after effects, so whether you do the data in excel or notepad does not matter much (as an example see this video, not much excel*).
How do you animate graphs? You animate them the same way you animate anything else there is no general one rule fits all solution here really depends what you want to animate.
But generally you want to write a script and or expressions to do it. Although you can do it a bit simpler too just select the graph right click and copy. It in Illustrator, separete the parts, save, then import the AI to AE. (or copy items to shape layers).
* Personally wouldn't do it this way as its way too manual. Too much a if all you have is a hammer kind of solution. There are better ways, but that's just me.