Google Maps API Key

Hi, I am trying to embed a google maps location into my website. I realise that I need an API key but am not sure where in my code it needs to go Can you tell me where I should paste it please? <script src='https://maps.googleapis.com/maps/api/js?v=3.exp'></script><div style='overflow:hidden;height:440px;width:700px;'><div id='gmap_canvas' style='height:440px;width:700px;'></div><div><small> embed google maps </small></div><div><small>disclaimer generator</small></div><style>#gmap_canvas img{max-width:none!important;background:none!important}</style></div><script type='text/javascript'>function init_map(){var myOptions = {zoom:11,center:new google.maps.LatLng(52.7224021,-1.3740620999999464),mapTypeId: google.maps.MapTypeId.ROADMAP};map = new google.maps.Map(document.getElementById('gmap_canvas'), myOptions);marker = new google.maps.Marker({map: map,position: new google.maps.LatLng(52.7224021,-1.3740620999999464)});infowindow = new google.maps.InfoWindow({content:'Coalville Acupuncture<br>Belvoir House, Belvoir Road, LE67 3PN<br>'});google.maps.event.addListener(marker, 'click', function(){infowindow.open(map,marker);});infowindow.open(map,marker);}google.maps.event.addDomListener(window, 'load', init_map);</script>