如何使用谷歌地图选择我的地理位置

I am new to geo locations and I am using PHP. I want to get a map on my website in web where a person in my website knows his exact location. He should also be able to change his location on the map like as in swiggy.com

Ok, I will asume you've read the Google Map API documentation. Googling what you're asking should drive you here:

https://developers.google.com/maps/articles/geolocation

What I'm gonna tell you is how to add a Draggable Marker.

  var map = new google.maps.Map([...])
  //After using geolocation and getting the user coordinates

  var marker = new google.maps.Marker({
    //Note this variable contains the previously created LatLng Object
    //with the user position
    position: userPosLatLng, 

    //Important so the user can realocate
    draggable: true,

    map: map,
    title: 'You're here'
  });

You want to update the user coordinates when he stops dragging the marker right?

Here you do it. Add this event listener after the previous lines:

google.maps.event.addListener(marker, 'dragend', function(event) {
    userPosLatLng = event.latLng;
});