Any number of ways to put two images side by side. One way shown in the video.
Arrows: There are several scripts and plugins from over-complicated to over-simple to make an arrow. This one is mid-range https://www.gimp-forum.net/Thread-Arrow-Script download the zip, unzip, put arrow-set-size.scm in C:\Users\"yourname"\AppData\Roaming\GIMP\2.10\scripts
Totally forgot the Rectangle
Make a new transparent layer. Draw the rectangle with the rectangular select tool to give a selection. Use Edit -> Stroke selection for the outline. Uses the FG colour. Turn the selection off Select -> None Why use a new layer ? Easy to delete and start again.
Video demo 4 minutes: https://youtu.be/Gej3E_Az0aM
Should get you started. The best way to learn Gimp is dive in and experiment.
Arrows: There are several scripts and plugins from over-complicated to over-simple to make an arrow. This one is mid-range https://www.gimp-forum.net/Thread-Arrow-Script download the zip, unzip, put arrow-set-size.scm in C:\Users\"yourname"\AppData\Roaming\GIMP\2.10\scripts
Totally forgot the Rectangle
Make a new transparent layer. Draw the rectangle with the rectangular select tool to give a selection. Use Edit -> Stroke selection for the outline. Uses the FG colour. Turn the selection off Select -> None Why use a new layer ? Easy to delete and start again. Video demo 4 minutes: https://youtu.be/Gej3E_Az0aM
Should get you started. The best way to learn Gimp is dive in and experiment.