It depend on the characteristics of the signal you want to generate.
A basic approach, with only 'native' VeriStand components: use a calculated channel to compute the value of a sinewave (for instance) according to the system time. You can use user channels to define amplitude and frequency, and use it in the formula for more flexibility. Then, map this calculated channel to a DAQmx analog output. The refresh rate of the output will be the same rate as the Primary Contol Loop of your target in the system definition (one new sample for each PCL iteration). Thus, it will work for 'low frequency' signals to generate.