Yes, you can upload Zip files on TES. This option allows you to upload more resources in less time. You just need to follow the usual steps you follow when you upload a normal file.
Find the steps here: http://help-resources.tes.co.uk/customer/en/portal/articles/1799273-how-do-i-upload-a-resource-?b_id=6050
For preview images, we recommend uploading an image file to act as a cover at the time you upload the Zip file. Zip files can not generate cover images.