Anyone can use the following 'live' GISsurfer map to help learn about U.S. National Grid (USNG) coordinates. This map with a USNG grid will work in most browsers on most devices including cell phones.
The map is displayed by GISsurfer which is a general purpose web map based on the Leaflet map API (Application Program Interface). For a description of all the features of GISsurfer that support U.S. National Grid coordinates (search, geolocation, etc) and links to USNG videos plus other educational material, please download the USNG and MGRS Coordinates pdf file.
As you zoom in the grid will become more detailed. Note that different basemaps let you zoom in different amounts. Use the Menu button to toggle the USNG coordinates grid on/off.
While the map is open you can now display data from *any* public-facing (i.e. no login required) ArcGIS server along with a USNG grid on top of that data. To get started, click the basemap button (next to the 'Menu' button) then under the 'Overlay' heading, click "Add GIS overlays". In the popup that appears, click 'Help'.
For more information about GISsurfer, please visit the GISsurfer homepage (you will be redirected).
Up until the middle of 2018 the map on this page was based on the Google map API (Application Program Interface). But that year Google started charging $$$ for its API use on popular web maps that got a high volumn of hits. As a result, the web maps I produce are now based on the free open-source Leaflet map API.
And if you would like a web app for your smartphone that will display your USNG coordinates and the equally important accuracy value, then take a look at FindMeSAR (https://findmesar.com). The "Tips" button has more information about this web app.