Google maps are copyright - and so technically not legal to use.
However you could use OpenStreetMap instead. Their maps are free to use for any purpose, under an Open licence. To keep it simple, just take a screenshot, paste into the software of your choice and add annotations.
If you want to take it a little further, depending on your level of expertise, it's also possible to download the map as an SVG. Then you could open it in a vector image editor such as Inkscape (which is free), or in Adobe Illustrator, if you have access to that software.