To get started with creating a custom map on Google My Maps, you first need to sign in to your Google My Maps account. Click on the three vertical dots at the top right corner of any map page and select "Settings." Scroll down to the "My Maps" section and click on "New Map." Next, enter the address or location of the plumber's business in the search bar and click on the "+" button. You can also add a title for your custom map by entering it in the text box at the top of the screen. Once you have created your custom map, you can use various symbols to indicate different types of businesses. For example, a circle with an "X" inside will represent a plumbing service. To add more details, such as phone numbers and addresses, click on the three vertical dots next to each business and select "Add Marker." You can also customize your map's appearance by clicking on the gear icon at the bottom left corner of any marker. Select "Edit Marker" to change its color, size, or shape.