Size elements individually
To size a single element, just click on the element and use the size bar. For an image/icon with a caption, you can click on it and adjust size for the image/icon and text separately.
Size all elements on the slide at once
Go to the Slide Options menu at the bottom of the slide. There's a size bar to edit all text elements and all image elements at once. Learn more about the Slide Options menu here.
Moving elements is as simple as just dragging them. Click on the element and drag it to the desired position. If you hold the Shift key while dragging, the element will be automatically aligned on X/Y axis as you move it.
To reset the element to its original position, click on it and hit Reset position.