You don't need to read out the full reference, but it can be useful to say something a little more akin to spoken word. So for example if you had paraphrased or quoted something from John Smith, or mentioned a theory he had created, you would put the in text reference next to the part on the slide which has this quote or paraphrase or theory (e.g. (Smith, 2022)). Then when presenting you could just say "Smith says" or "Smith discusses" or "Smith argued", just to ensure that you are making clear that it isn't your own idea.
Hope this helps!
-Laura (Lancaster University Student Ambassador)