Layers are great, but there are a few tricks to know. Remember, if the video goes too fast for you, remember you can pause it. In this example we are using a frame to make an about image for the sidebar.
Click create a design, then use custom dimensions. You want to make sure that your canvas has the same dimensions as your frame. To find out what those dimensions are, find your image and click on it. Then press CMD+I (on Mac) to see what the dimensions are in px. Type those dimensions into your project, and then Design!
Next, you need to upload your images. The Upload button is at the bottom of the sidebar on the left. One uploaded (how cute is that duckie!), simply drag and drop onto your design. You will see that your frame is transparent in the middle. Position it on top using the Arrange button in the top right toolbar. You'll find that if you drag your images too far off the canvas the arrange option disappears. Don't worry too much about having everything neatly at the edges as you can trim it all later in wordpress > edit image once it is uploaded. Just focus on getting the layering right.
You can change which image is in front by using the arrange button in the top left corner.
Once done, click Untitled Design up the top and give it a name. Then click Download, and download as .png.