how to check the oil at rear gear or differential on 2001 Dodge Ram Van 2500

how i will check the oil of my rear gear(just to make sure it is not leaking? and if the rear gear blew the oil, is that possible or it can be still move by driving on it? or it will not gonna move at all?

Asked by for the 2001 Dodge Ram Van 2500
With your vehicle on a level surface, remove the rubber plug on the differential cover. Poke the tip of your finger into the hole, the proper oil level is about 1/2" below the lower portion of the filler hole. While you are under the vehicle, look around the cover and pinion areas for leaks. If you have a leak, it will be very obvious. You can still move the vehicle with little or no lubricant, but damage to the bearings and or gear set may have set in. If the differential is noisy while driving (growling or whining) it is a good indication of bearing failure.