In order to do multi variations like (select color or size) you need to start with a new listing from the beginning, and then look just below the title section of the advanced listing tool for the word Variations.
Then click the arrow next to the word and it will open up some options and then fill out the rest of the form.
Keep in mind that not all categories of item has this feature available so if you do not see the option where I indicated then it probably is not available for your category.
Good Luck Selling!
