Add and Edit Portfolio items
Going to the portfolio section is from clicking on your portfolio link in the header navigation or from Pages -> Portfolio. Note that some portfolio sections might be renamed depending on the theme but it's always marked with the icon 'P'.
After that click on 'Add Item' to add a new portfolio Item. You got the option to add Image, Gallery or Video as portfolio item. Title and Description are also options which you can show or hide from the settings below. Show image in lightbox will add a zoom button when hovering the item with the mouse to expand in full screen.
Show description in popup will show a summary of portfolio item + title and description in a nice popup. Example below:
You can also add filtering categories for your items. Simply click on 'Categories' and add or select already added categories.