Dynamically adding JSON data to embedded google map

This is probably quite a nooby question but I am new to this and here to learn so please be nice.

The web application I am developing has an embedded google map that I want to add some custom locations dynamically to using JSON data from a different page.

There will be two JSON files. The first one will have a set number of items and will remain unchanged. Each item inside will have coordinates, a name, and possibly a description (I haven't decided yet).

The second JSON will start off empty and be added to by the user. They will record coordinates, a string to use as a description, and none or more images (also stored as strings). They can record any number of these objects inside the JSON

What I want to do is overlay these on the map possibly by adding a container showing the JSON data when hovered or clicked. This has to be done dynamically so that when data is added/removed from the second JSON the map will change to reflect this. This doesnt have to be live updating and can be done by refreshing/reloading the page.

Like I say please be nice, I am here out of interest, just to learn.