From the Navigator

On the Navigator ribbon, click Content tab, and then locate multimedia. Select one or more and then drag over the empty space of the article tree.

From the Shell main tab over Clipboard

On the Shell main tab, click the clipboard icon in the listing on all elements to select. Return to Articles main tab, and then drag from the Clipboard tab on the empty space of the article tree.

From the Shell main tab directly

On the Shell main tab, select one or more multimedia items, and then drag over the label of the Articles main tab, hold while it switches to the Articles main tab, and then drop them to the empty space of the article tree.