Markers Google Maps V3 JavaScript

var map

function detectBrowser() {
  var useragent = navigator.userAgent;
  var mapdiv = document.getElementById("map_canvas");

  if (useragent.indexOf('iPhone') != -1 || useragent.indexOf('Android') != -1 ) {
    mapdiv.style.width = '100%';
    mapdiv.style.height = '100%';
  } else {
    mapdiv.style.width = '600px';
    mapdiv.style.height = '800px';
  }
}


function carregarMapa() {

    lat=document.getElementById("txtLat").value;
    lng=document.getElementById("txtLng").value;

var myLatlng = new google.maps.LatLng(lat,lng);



var mapOptions = {
    zoom: 16,
    center: myLatlng,
disableDefaultUI : false

  }

var map = new google.maps.Map(document.getElementById('map-canvas'), mapOptions);

  map.setOptions({styles: [
    {
     featureType: "poi",
     stylers: [
        { visibility: "off" }
     ]
    }
 ]});

}


function criaPonto(){

plat=document.getElementById("txtLat").value;
plng=document.getElementById("txtLng").value;

var myLatlng = new google.maps.LatLng(plat,plng);



var marker2 = new google.maps.Marker({
  position: myLatlng,
  map: map,
  title: 'Título Restaurante Y'});

}
google.maps.event.addDomListener(window, 'load', initialize);

Hello, I created this code in javascript trying to create a google map where I can load markers, so far, I only managed to create markers if I reset the map, and the idea was to create these markers at runtime. For example: I would create a marker if it was X away from the point my sensor located, otherwise that marker is not displayed.

The issue has been resolved! Thanks for the help from the user: link That was very present and managed to explain my mistakes.

Thanks!