Go to https://smallpdf.com/word-to-pdf in your computer's web browser. It's in the middle of the SmallPDF page. Doing so will open either a File Explorer (Windows) or a Finder (Mac) window. Go to your Word document's location, then click the Word document to select it. It's in the bottom-right corner of the window. Doing so will upload the Word document to SmallPDF. On a Mac, you may click Choose here instead. This option is in the lower-left side of the SmallPDF page. Your PDF will download onto your computer, though you may have to select a storage location and/or confirm the download depending on your browser's settings. It may take a few seconds for this option to appear if your Word document is large or your Internet connection is slow.

Summary:
Open SmallPDF's Word-to-PDF website. Click Choose file. Select your Word document. Click Open. Click Download File.