Setting up MapServer WMS and use it with OpenLayers

I have set up MapServer WMS on the localhost by the following map file:

MAP
  NAME "Prvi_WMS"
  SIZE 600 300              # 600 by 300 pixel image output
  PROJECTION
       "init=epsg:4326"

  END  
    #EXTENT -180 -90 180 90
    WEB
    IMAGEPATH "/ms4w/tmp/ms_tmp/"
    IMAGEURL "/ms_tmp/"
    METADATA
      "wms_title" "My Global Map WMS Server"
      "wms_onlineresource" "http://localhost/cgi-bin/mapserv.exe?mode=map&map=c:/ms4w/Apache/htdocs/MapFile06_wms.map&"
      "wms_enable_request" "*"
      "wms_srs" "EPSG:4326"

    END
  END

  LAYER

    NAME countries
    TYPE POLYGON
    STATUS DEFAULT
    DATA "/ms4w/data/countries_simpl.shp"
    MINSCALE 1000

    MAXSCALE 1000000000     
    PROJECTION
       "init=epsg:4326"
    END  
    EXTENT -180 -90 180 90

    CLASSITEM 'NAME'
    CLASS
      NAME 'Bulgaria'
      EXPRESSION 'Bulgaria'

      OUTLINECOLOR 100 100 100
      COLOR 255 255 150
    END

    CLASS
      NAME 'All Countries'
      EXPRESSION ("[NAME]" ne 'Bulgaria')
      STYLE
        OUTLINECOLOR 100 100 100
      END

    END
    METADATA
      "wms_title" "World Boundaries"
      "wms_onlineresource" "http://localhost/cgi-bin/mapserv.exe?" 
      "wms_srs" "EPSG:4326"
      "wms_enable_request" "*"
    END
  END
END

then, I checked GetCapabilities and GetMap requests and the results seem fine. However, I have problems getting the map inside the OpenLayers. Here is how I define my WMS layer:

    
    


    


    
Primer prekrivanja slojev in izbire podlag
    

The WMS layer shown in OpenLayers is completely white. What am I missing?

Answer

You say you have checked the GetCapabilities and GetMap requests/responses which indicates you are running MapServer as a WMS. Thus you need to be using a WMS layer in OpenLayers - I'm not sure of the status of the MapServer layer. so you need something like:

    map = new OpenLayers.Map( 'map' );
    layer = new OpenLayers.Layer.WMS( "OpenLayers WMS",
            "http://vmap0.tiles.osgeo.org/wms/vmap0", {layers: 'basic'} );
    map.addLayer(layer);

UPDATE

You'll need to provide a wms_srs element for each projection you need in your map file to enable reprojection (see http://mapserver.org/ogc/wms_server.html#setting-up-a-wms-server-using-mapserver)