Do you mean tethering a wifi only iPad to an iPad that has a cellular data connection?The new iPad+cellular has a wifi hotspot capability,if your cellular service provider supports it.If so,you can turn on the hotspot and your wifi only iPad should be able to connect.This hotspot capability only applies to the new iPad.
If you have a Verizon version the new iPad and a cellular plan with it, then your wifi only iPad can get to the internet if you use the hotspot feature on the new iPad with the cellular plan. On the Verizon version, the hotspot feature is turned on at no extra charge, but you have to have the cellular data plan.