Just go through the list of your Critical business functions and decide what is crucial for you business to operate and how you would recover if that thing were to be destroyed. Like for example you have a AD server that also does exchange and you need email and login information at all times. You would state in a disaster recovery that you would use your backup solution and a new machine to roll over the back up and have that server up and running in X amount of time. Or if it has to be up 100% of the time maybe state how you have a off-site replication solution. It basically needs to be a outline of what would you do in case of a certain disaster like a fire, tornado, theft, or just fails to function. You can pull up templates or examples to see how they are laid out but generally you just state how you would recover your network infrastructure in case of each disaster scenario. Also included in the recovery you can include preventative measures and detective measures like installing UPS and generators to prevent your machines from ever shutting down. Or having a hard disk monitor running to alert you before your hard disk dies. It is basically a plan on what to do to prevent a disaster from affecting your business.