Task: I would like to use the show app to add the first vedio from vedios section to the third slide of the presentation
Steps:
click on the plus icon ( add on) at the lower right corner of the page to add new slide 
click on the first option ( title slide ) at the screen to add new slide 
click on the plus icon ( add) at the top of the page to insert video in the slide 
choose video button at the top of the screen to insert video in the slide
click on add video button at upper left side of the page to insert video in the slide 
choose first option available at the screen under recent files