When you start the negotiation, you must enter a value in the space where it indicates "main variable". Thereafter, you will have to figure out which additional variable to add, by clicking on the "Add variable" button, and entering a possible variable. If the variable you have entered is correct, the system will offer you several options of that variable to choose from and you will have to choose the one that best suits your proposal.
If you have doubts, you can re-consult the interests and concerns of the negotiator by clicking on the "notebook" button on the right hand side, if it appears blank it will mean that you have not talked enough with the negotiator to discover their interests. Remember that all the variables can be deduced by reading the case with attention through the "Menu" button - See case.