To use the dining plan credits you will have to link your resort reservation number when making the CRT reservation. If you're making the res online there is a blue link at the bottom of the res page that says something to the effect of "I want to use a dining plan for this pre-paid reservation." Click on the link and input your resort res info. On the final page the total to be charged to your cc should be $0.00. If you are calling to make the res you will need to tell the CM your resort info.
Either way you will need to give cc info to guarantee the res.