How to display two stimuli at once a time in psychtoolbox

I am trying to display two stimuli simultaneously on the screen. first for the participant, and later for the photodiode in the bottom corner of the screen. I have tried to use ‘DrawTexturs’ but I don’t know how to use it and its options.
Am I using the right method at all?!

Possibly. But sounds like you’re completely new to psychtoolbox. Have a look at some demos that will show you how to use ptb, and see