To add additional elementos just go to respective page u want to edit and click on edit with elementor
The elements panel is on the left side of the edit page
to add new element just click on the plus icon on the lower end of the page and drag and drop an element u want to add. For example if u want to add an image add a new section by clicking the plus icon and select the single column. search for image in the elements tab and drag and drop the image element. upload an image and edit accordingly.