For this post we are going to use https://www.weather.gov/gis/WebServices which is repository of government weather data. First select the layer you want to add to Scribble Maps.
Next, Click "WMS"
Now visit the Scribble Maps editor add click the "+" button in the bottom right next to Base Layers.
Next select "Add WMS"
Now paste your URL into "WMS URL" select your layer and then hit "Add WMS Layer"
Close the window and you will now see the WMS layer added to your Scribble Map!
The great part of WMS layers is depending where you get them from they can update every time you refresh the map. If the WMS layer provides up to date data, you do not need to save the Scribble Map to get the most recent data.
If you are more technical, you can use https://mapserver.org/ to publish your own WMS services to be used on ScribbleMaps.com as well.