Start an Import task and in the "add file" section choose the Google Drive URL as a source type.
Fill out the URL field and choose the correct file type and press "Download".
If your supplier gives more than 1 file, for example 1 for the products, 1 for the inventory and 1 for the pricing, click on the "Add more files" option and Syncee will treat them as 1 complete file. You just have to map the files correctly in the "Field Mapping" step. The most important thing is that, one import task must belong to just one supplier.