I don't know anything about the flash you have purchased, so I can only give a few suggestions. Many flash attachments have a "slide rule" guide that you can set the ISO you are using and then it will give you the automatic flash distances and the appropriate aperture settings. If your flash doesn't have such a guide on it, then about the only thing I can suggest is for you to set the flash to the "Automatic" mode, connect it to your camera, and take a bunch of test shots at different aperture settings to see which aperture settings works the best at different ISO settings. That would be a trial and error way to find out where it would perform the best.
If you can find out what the guide number is for the flash, that would give you an indication of where to start. For instance, if you discovered that the guide number is 120 for ISO 100 (just as an example) you could set your camera at ISO 100, aperture preferred automatic mode. Divide 120 (or whatever the guide number is) by the distance to your subject, and that will give you the proper f-stop to use. Other than that, just experiment in the automatic mode of the flash and aperture preferred mode of your camera to find out which settings work the best.