artificial neural network using MATLAB

Hi, I am using neural network in my project for simulation. I am new to this. I am using ANN in MATLAB (2009b). I have 3 variables as my input- air flow rate, liquid flow rate and liquid concentration, and 1 output- pressure drop. Please tell me how to proceed because when i tried, i encountered some problem. It said input has 3 rows which does not match with the output-only 1 row.
Please reply soon. I need it urgently as it is very crucial for my project.