The easiest way to insert an image in your document is to use the Add image button found in the toolbar. After doing that, you still have to specify the graphic file which is the source of the image. Generally this is done by first clicking on the image placeholder icon and then using the Attributes tool to specify the graphic file. DocBook example: clicking on the image placeholder selects the corresponding imagedata element. Then you have to specify a fileref attribute for this element.
Inserting image in a document is a very common task that's why there are more convenient ways to specify the graphic file which is the source of the image:
In both cases, this displays a specialized dialog box.
The "Source location" field allows to specify the graphic file which is the source of the image. The "Destination location" field allows to specify how this graphic file is to be referenced in the document. Note that this dialog box requires specifying URLs and not filenames.
For example, let's suppose that your document is found in the docs/ directory and that all your graphic files are found in the docs/images/ subdirectory. If you want to insert an image pointing to docs/images/logo.png, then simply make sure that the "Reference as" radio button is checked.
Now let's suppose you want to insert C:\tmp\screenshot.png in your document. You'll probably want to copy this file to docs/images/ subdirectory and give it a more meaningful name (e.g. login_dialog_box.png). This is done by checking "Copy to" and specifying "images/login_dialog_box.png" in the "Destination location" field.