Print this page as PDF. You can do this using the built-in "Microsoft Print to PDF" on Windows or the "Save as PDF" option on macOS. Make sure to disable "Headers and Footers".
Add all the receipts to the PDF file (this can be done in Adobe Acrobat DC or Preview on Mac). In case of an invoice you paid, please add a bank transaction screenshot ("bankafschrift", can be exported from most banking applications).
Email the declaration form PDF to firstname.lastname@example.org with subject "Declaration < activity >" (where < activity > is the activity you're declaring.)