There are various ways to establish a radio link between two Arduinos, using XBees is one solution. Which options available to you will depend on constraints such as range, cost, available power.
Given two Arduinos with communication between them, you can implement sketches that allow them to collaborate. For example, control inputs on one Arduino could cause actions on the other - but it is up to you to design the sketches and hardware correctly to achieve this. It's a little harder than putting all the functionality on one Arduino but not a lot harder, so it would be sensible for you to tackle the problem in small steps - get the functionality you want on a single Arduino; get radio comms working; split the functionality between the two Arduinos connected via radio.