I have a text list of 160 names and addresses. How do I format it and print on Avery 5660 labels without having to enter each name and address in a new spreadsheet?

I have Libre Office 5.1

If your data (names and addresses) are well structured it should not be a problem to get them into a table in ‘Writer’ using > ‘Table’ > ‘Convert’ > ‘Text to Table…’. This table you may copy and insert into a new ‘Calc’ spreadsheet without any typing. The spreadsheet you can use as the data source when defining the ‘Writer’ document for printing labels using the > ‘File’ > ‘New’ > ‘Labels’ tool.

Read the manual - it is fully described there.