How can I plug my 3 prong dryer into a 4 prong receptacle?
You'll simply have to purchase a 4 prong dryer cord, which can be found at any local hardware store or big box store.



Then follow the dryer manufacturers installation instructions for connecting a 4 prong plug.
Most dryers will be wired similarly to the one described in this answer, though it could vary a bit from manufacturer to manufacturer.