Hello,
Use the syntax below to customize options for your feedforward neural network.
net=feedforwardnet(size,trainFcn);
The syntax above generates a feedforward neural network and stores it into net. THe number of hidden laters are "size". "TrainFcn" is the performance function for feedforwardnetwork.
Also , please take a look at the following answer
To get more information about feedforwardnet click link