Uploading .csv - more or less working but...

I have eventually got some products to upload via .csv but I have still got some problems. I've studied various example and test .csv files and I can't work out what I am doing wrong!

-the product titles and prices are working but nothing else - no descriptions, sizes (I was expecting them to appear on the item's listing) nor categories

- the image urls are not uploading the image files. These are currently Google Drive and I've tried setting them to allow sharing. They do end with .png (However to be honest I'm more worried about the description and size and category not working.)

Also just a general question, if I upload another .csv with different products will it wipe out the old ones?

Thanks