Open Street Map came into existence when map data source was controlled by private & government bodies, but now times have changed it’s now an editable map made with the efforts of online masses/volunteers.
The simplest difference between an open street map & google map is, any edit you make in OSM is owned by you only whereas those done on Google Map is owned by Google.
How would you setup and open street map using Mighty Addons is the big question. You can easily add locations in your map with the help of latitudes & longitudes coordinates. First step is to go on and add the OSM widget on your page. Then go to Content tab > Open Street > Locations.
Add item, enter the Latitude & longitude values which you can get from here.
Choose whether you want to show the Info Window or not. For info window popup styling related options, checkout this article.
Select your Marker icon, either default or add a custom icon, and the set the Marker size.
Similarly you can add any number of locations you want to in the map. To know more about other Map options read those articles.