I would use an example (Help >> Find Examples >> Hardware Input and Output >> DAQmx >> Analog Generation >> Voltage >> Cont Gen Voltage Wfm-Int Clk-On-Board Regeneration.vi) to help understand how to write a waveform through an analog output channel. Change the physical channel control to accommodate for both AO0 and AO1 (e.g. “Dev1/ao0:1”). Change the DAQmx Read to accommodate for a 1D array of waveforms. Then build a 1-D array with two waveforms and wire the output of the array into the DAQmx
Most DAQ boards have a limited onboard memory or First In First Out FIFO (e.g. 622X has 8,191 Samples). If you want to only use the onboard memory, make sure that your samples for each channel is less than 4,095 samples per channel. If you want to use more samples than 8,191 total both channels, then you would want to wire a false constant into the property node (AO.UseOnBrdMem).
What is the acquisition mode for both channels? If you set it to continuous, then you will have to start writing samples to the FIFO before you execute the start task. Otherwise, you should get an error.