Please follow REDI API Quickstart to enable access.
Next, please download REDI API Excel Examples.
Then, the relevant examples to review and run are "Quote Monitor - DDE Equities" and "Quote Monitor -DDE - US Options".
Please note for completeness: to be able to access market data, REDI user needs to be permissioned to access market data.
I am sending and canceling orders via excel VBA and Redi on 150 stocks. Redi crashes after a certain period of time, I will often get this response "Microsoft Excel is waiting for another application to complete an OLE action."