It would be useful for you to upload your current experiment and conditions file so we can see what you have done so far.
If you are using Builder to create your experiment, you could define your positions in your conditions file, and call position variables for each stimuli. For example, if you had a shape stimuli, that you wanted to randomly alternate whether the shape appears on the left or right of the screen, you would create a column in your conditions file called xPos and in cell for that column, for each trial declare a position i.e., .5 for the right hand side, -.05 for the left hand side. In your shape stimuli, add your Xpos variable to the x coordinates of the “Position[x,y=]” parameter, e.g., ($Xpos, 0). The stimuli locations will be randomized by selecting “random” as your order in your loop properties, where you define your conditions file.