The screw on the left is the idle stop screw. Adjust it so the engine stays running but not at excessive rpm when the throttle trigger is released. You need to pull and release the trigger after each adjustment so the lever comes back to rest at its new position on the stop screw. There isn't a number of turns for these.
The screw on the right is the idle mixture screw. When there are two mixture screws the other one is high speed mixture, when there is only one it is always low speed. If it runs OK fast but not slow that often can be fixed by adjusting the idle mixture. Warm up the engine and keep it running by pulling the trigger as needed. Adjust the idle mixture so it runs better slow. There will be a place where the rpm is maximized at idle condition (trigger not pulled or only lightly pulled). Once you reach that point, adjust the idle stop screw for a decent idle speed. That is about where you want except you may need to turn the mixture screw out (counterclockwise, richer) a little if it seriously hesitates to rev up and/or stalls when you pull the trigger off of idle.
Looking at the picture again though I kind of wonder if you really have a single adjustment carb, or a two-screw one with the high speed screw gone.