In Google map Custom fields are used to display infowindow contents of the posts.Custom Fields are associated with Posts. You can create unlimited custom fields and display them in info window. To add multiple ‘Custom fields’ you should do following steps :

Show Post Infowindow using custom field

Step 1It is hidden by default and you need to use the screen options at the top of the posts/pages and enable ‘custom fields’.
Custom Fields
After that, the box appears at the bottom of the editor screen.
Custom Field Box

Step 2Here, you can easily add any custom field you like. All you need to do is give it a name and a value.

Add Custom Field

Step 3Go to Add or Edit Map page and scroll down to ‘Infowindow Message for Posts’ and insert custom Fields placeholder.
* Use {%custom_field%} to display custom fields, in the infowindow content. In this e.g You can Use custom field as a placeholder like {%phone%},{%website%} etc. You can use your own html structure as well.
Infowindow Message Post

Step 4Click Save Map and open it in browser.
Your Post infowindow looks like :

Post Info Map

Video Tutorial