A marker identifies a location on a map. By default, a marker uses a standard image. Markers can display custom images, in which case they are usually referred to as “icons.” Markers and icons are objects of type Marker. Markers are designed to be interactive. For example, by default they receive
'click' events, so you can add an event listener to bring up an info window displaying custom information.
You can find more detailed information on Google page by clicking on here.
If you do not want to deal with coding, you can easily use DML Easy Google Map Plugin for your website or PHP project. It is very useful and has a lot of features.
You can check the other features here.