template for Avery labels

It might be as simple as downloading a blank template in .pages or .docx format from the Avery website. If the labels are to be all identical, then you create an appropriate sized text box, fill it with the return address info, and then duplicate that text box over all the template boxes on that label. Then save it as a template, so you don't have to do this again.

No version of Pages after Pages '09 v4.3 has offered Mail/Data merge to automatically populate fields that you position over labels and that are then populated from a spreadsheet. Word can do this with Excel. LibreOffice Writer can do this from their Calc spreadhsheet, or a LibreOffice database (requires installation of Java).

Such a frustration! Assuming that you have the data in Numbers or Excel you should be able to do it via Avery website. You will need to set up an account at www.avery.co.uk then there is a "Design & Print" page where you can choose your label and upload your data to do the mail merge.

It works well - better than using MS Word really.

The final print generates a PDF which you download back to your own computer before printing.