HOW TO MOVE, COPY AND INSTALL PATTERNS
Changing the desktop pattern, storing the pattern being edited, and editing one of the stored patterns follow one simple rule: 

Any double-outlined box, filled with a pattern, can be dragged to any other and will copy its pattern there, overriding any pattern already there.

For example, press the mouse button in one of the stored patterns on the right side of the window, drag the pattern to the Easel, then release the mouse button. You’ve just copied that stored pattern into the Editor, where you can modify it.

Dragging the patterns lets you accomplish many things:

Drag a pattern from the Easel or one of the Stored-Pattern Spaces into the Little Mac Monitor (LMM) and it will be copied to the LMM, becoming the current desktop pattern.

Drag the current desktop pattern from the LMM to the Easel and it will be copied to the Editor, ready for modification in the Editor.

Drag a pattern from the LMM or the Easel to a Stored-Pattern Space and you’ve copied the  pattern to one of the Stored-Pattern Spaces to keep it readily available.

Drag a pattern from one Stored-Pattern Space to another Stored-Pattern Space to make a duplicate copy of it.

Dragging in all these instances retains the original pattern and creates a copy in the new place, copying over the pattern in the destination position. But there is one extension to the rule:

Dragging a pattern from a double-outlined box out of the window clears the box. If you drag a stored pattern out of the window you’ll clear its space. If you drag the Easel’s pattern out of the window, the Editor is cleared to the currently selected color.

There is also one caution:

COPY WARNING
If you have not first saved the pattern to disk, you will lose it by removing it from its position in the Wallpaper Control Panel.

Drag the Little Mac CPU (LMC) to any doubly-outlined box in the Wallpaper window to invoke a load dialog to load a pattern to that box. Drag any pattern in the Wallpaper window to another, to load the first pattern to the second box.

Dragging is the slickest way to install patterns, but it isn’t the only way. Patterns can be loaded to any selected double-outlined box in the Wallpaper window via the Load menu command, which you can invoke in other ways than dragging the LMC to the position to which you want to load a pattern. You must first select the position to which you want to load, by clicking on it once. Its double-outline will become black. Then you can select the “Load” menu choice or type the keyboard command of the character “L.” Under System 6 you can also type Command-L. System 7 doesn’t support menu commands in cdevs at this time.