If you have a file to attach to your ticket, you can do so on the final ticket submission page. You can either drag and drop the file into the upload box or click on Select Files to Upload to search your computer for the file in question.
Any file that you successfully upload will display above the upload field. Additionally, if you need to remove any uploaded files you can click on the red trash can next to the file name prior to ticket submission.
Please note that you are not limited to adding files only when submitting a ticket. You can also upload a file to a ticket that has already been submitted by dragging and dropping the file into a comment in the ticket Timeline section.