From the components palette, drag and drop the item you want in the canvas. Once inside the canvas, you can re-size and move it to fit in your design. To move it, select it and drag it to the desired destination; you can also push it with the arrow keys (holding down the SHIFT key will speed it up). To help you debug your design, you also have the following instruments:
The automatic alignment system (green guidelines).
The grid (see Mesh).
The Rulers.
The Guides. To position them, click on the rulers and drag them to the desired place. To delete them, simply select them and press the "delete" key.
There is a toolbar related to the work area. The zoom indicator is on the right side: magnify or reduce the size by using this drop-down menu.
The elements on the screen keep a certain order of depth between them. You can see the order in which they are arranged in the Outline of the current screen. Thus, the highest ones block out the ones below them. To change this order, right click the item (or select it in the outline view) and select the Order option of your choice. You can also drag and drop within the Outline view to reorder the elements in depth.
The Image component allows you to see which parts of the screen will be taken up by images. Or you can replace these pictures with real images by selecting a file from the Properties view, by double clicking on the image, and right clicking on the image and selecting 'Image -> Browse...'
Create more screens in your prototype by clicking the "+" button on top of the list of screens.
Rename it by right clicking it. Select Edit from the context menu.
If you want to delete one, right click it and click Delete.
And, to edit the content of an inactive screen, double-click it from the list of screens. Its content is then loaded onto the canvas where you can easily change it.
Justinmind Prototyper allows you to copy and paste screen components within the same screen or onto other screens. You can use the options in the Edit menu or the usual keyboard shortcuts of “Ctrl+C” (copy) and “Ctrl+V” (paste). To duplicate elements, drag them to the desired position by holding down the "Ctrl" key or with "CTRL + D" (Mac keyboard shortcuts are different: cmd+c, cmd+v and cmd+d respectively).
Remember: Whatever action you do, you can undo it or redo it from the Edit menu (and with the shortcuts "Ctrl+Z" to undo and "Ctrl+Y" to redo).