For example, I have a spreadsheet where I want to log my workouts. I have a shortcut that opens numbers and adds a blank row and that was easy to make. But now I want to add the current date in column A of the new row and I've never been able to figure that one out.
For your shortcut, without knowing the specific step you're stuck at, first get the current date. You'll then want to format the date using the Calender->Format Date block, setting the custom format to what you need based on these rules: https://www.w3.org/TR/NOTE-datetime-970915
I don't have Numbers, but maybe figuring out A1 spreadsheet notation might help.
My general tips: use a whiteboard or a notebook to sketch out your pipeline, study other people's Shortcuts to learn new tricks, use the alert and exit blocks to debug stuff and finally, make sure you're coercing/casting data into types that Shortcuts can use (Scripting->Get Type will help).