This requires some practice, but no worries: It’s really not that difficult.
As with everything, you just need to try it! Once you’ve got it down, there’s nothing to it.
Hold an oyster in your hand, wrapped tightly in a folded dishcloth. The flat half of the shell should be facing up. Stick an oyster knife—or another sharp, short knife—in the hinge, the point were the two halves are attached. Sometimes it takes some effort to find the right spot. Carefully stick your knife inside and gently pry the two shells apart. Slide the blade along the edge of the shells. Twist the knife to open them. Make sure you hold the oyster horizontal or you’ll spill the oyster “liquor.”