Entering jazz solo suggestions for beginners

Maybe with an image?
Or, press Z and search notes, then drag (I attach a test)

You could enter the notes normally then mark them stemless in the Inspector. The box could be added as an image, or a a boxed text as shown above, or maybe you could just draw lines from the Lines palette.

Slightly different approach: (EDIT: not so 'different' as Marc was faster now :) )

1. Start with the measure filled with slashes (Edit > Tools > Fill with slashes)
2. Select the first slash in the measure and enter note entry mode by pressing N
3. Enter your notes (assuming a measure of 4/4, you'll want to enter them as 1/8th notes, starting with a rest): 4, 0, A, C, D
4. Select the rest and make it invisible, either by using the inspector (F8) or by pressing the shortcut V
5. Select your notes (click first note, shift-click last note)
6. In the Beam Properties palette, double-click No Beam
7. In the Inspector press the Notes button
8. Under the Chord section, tick Stemless
9. [optional: under the Note section, untick Play to prevent playback by MuseScore of those notes]

Now as for the box around them, that is currently a little bit of a hassle, but the closest I got was using 2 plain lines from the Lines palette. The show up on the bottom left of that panel if you're looking at the Advanced workspace (see the dropdown selection box at the bottom of the palettes window to switch there).
First I've aligned the top line:

1. drag and drop the line to the first note
2. double-click the line to enter its edit mode
3. UseShift+right arrow to adjust the end reference point of the line
4. drag the handles and use the inspector to position the line as the top line from your box, make sure Allow diagonal is active in the Inspector
5. right-click the line and open up the Line Properties…
6. Switch on the Hook property for the Begin and End section, with a height of 4.00sp (which equals the standard staff height)
7. Adjust the Line thickness as you please, I've found 0.25sp to be quite a nice value for this situation
8. Drag and drop a second line, adjust its range and position in a similar fashion to make it the bottom line of your box.

See the attachment for an example of this method.