Multiple ways to zoom into Excel using the keyboard and mouse.
When you use the keyboard shortcuts, you will see a window like this:
You can then hit one of these keys and Enter to quickly zoom to a certain level:
1 - 100% zoom level
7 - 75% zoom level
5 - 50% zoom level
2 - 25% zoom level
0 - 200% zoom level
F - Zooms in until the selected cells completely fill the worksheet screen.
C - Allows you to enter a custom number for the zoom level.
Zooming in Excel is very easy but learning these few keyboard shortcuts will save you a lot of time when you have to do it often and will prevent you from interrupting any current workflow.