Airtable is actually a mix of a database and a spreadsheet, leaning a bit closer to the former. Data storage and manipulation is different than a traditional spreadsheet, so you don’t add summary rows to tally data. Rows are records, and records don’t have any knowledge of each other, so you can’t just sum a column (aside from the built-in summary bar at the bottom of the window)
You don’t need to do the count manually. If you each record in your main table links to an option record in the
[Options] table, you can then add a special field type called a Count field. That will use the incoming record links and tell you how many links there are for each record, which will let you know how many of each option are chosen in your main table.
I’m short on time at the moment, but if that doesn’t clear things up, let me know and I’ll walk you through it in more detail.