Sorting?

I'm baffled & could use some help. I've learned how to filter records by clicking on the header in a table. And can sort ascending or descending. But I can't figure out how to construct a (relatively simple) sort that has several levels. For example, sort by one field first, then do a sort on a 2nd field (while maintaining the 1st sort). For example, sorting invoices by date, and then within each date sort by amount. I see instructions for doing more complicated things, but not for this (relatively?) simple process. 

TIA for any wisdom on sorting.