I'm new to Google sheets, and I've got this spreadsheet with some IMPORTRANGE functions in them, and they look like this:
=IMPORTRANGE($O$2; "Jan!B33")
That first value, $0$2, is supposedly the spreadsheet key, but I'm used to that spreadsheet key coming from the HTML, for example "1QCfFIx6evcghuH4k74_ksqx6P7sb5xzUpRaoQobV6MA", or something like that.
My question is, what is this dollar sign notation, and how do I use it? Is it even something from Google Sheets or is it something someone mistakenly copied from Excel or another program?