The Acquire | From Clipboard… function opens the contents of the Windows Clipboard in the Editor.
The Clipboard is where information goes when you cut or copy it in Windows. To place part of a picture in the Clipboard, select that part of it and then use e.g. [Ctrl+C]. That part of the picture is then placed in the Clipboard and can be pasted elsewhere in the picture, or in a completely different picture using e.g. [Ctrl+V]. You can also send a screenshot to the Clipboard by pressing [Print Screen].
If the Clipboard contains a picture, then you can use the Acquire | From Clipboard Browser menu item to open a new Editor window and paste the picture into it. To then save the picture in a format of your choice, use File | Save.