Karlie here from the Shopify Support Team! If you're looking to import products from another website, then you might be able to use a spreadsheet format to import them into your Shopify Admin. A CSV file would allow you to export the product information in a spreadsheet format and then import those products into your Admin.
You're going to want to make sure that when you import your CSV file into the Shopify Admin that the field headers are in the same order and each separated by a comma - I would recommend downloading the sample CSV, here, to make sure that your spreadsheet is formatted the same way. You can read all about how to export, import and format a CSV file in our handy help guide, here.
When importing your products into your Shopify Admin, you may encounter some issues with the CSV file. The Shopify Admin will tell you if there are any formatting issues with your file before it can correctly import. We have a guide, here, that will tell you how to solve common product CSV import problems.
I hope this has answered your question. If not, or if you have any further questions please let me know. I will be happy to help!
Hello again, @crowshead!
Karlie here! Yes, you can do everything using one spreadsheet. If you check out the Sample Spreadsheet from the guide that I had sent you, you can see all of the different columns for your product information. Category assignment would be Collections, but you can use the CSV to add in your product image URLs, prices and variants as well.