Add them in the right excel column

Note that you can add images and files from other websites, just type img:http://my-website/my-image.png or for files like this pdf example : pdf:http://my-website/my-file.pdf&&title of the file
For files, default prefix is file: but you can show specific icons using doc: or docx: or pdf: or xls: or xlsx: or ppt: or pptx: