Hopefully you see this.
Move your cursor around under the menu/nav bar of this page until you see the black bar pop up titled 'page content' - Click EDIT on that. That will put you into edit mode.
Welcome to edit mode.
Move your cursor around this white area. You will see black lines and bubbles pop up. Clicking the bubble will give you the option to insert objects, such as text, image, buttons etc. All options will be available for the ojbect in the pop up. The black line indicates where it will be positioned. Once you have inserted it, you can just drag and drop it around in different locations, indicated by the black lines. Best to get a bunch of objects on a page and shuffle them around to get an idea for how this works.
Once you hit SAVE up the top, the page is live. Then you can click the top left arrow to view the page full screen.
I've dropped in some objects for you to play around with below. Click Edit on any item for options - Keep an eye for CONTENT & DESIGN tabs up top. Feel free to get your hands dirty.