KR lens change problem

Im really new to dslrs and this is my first. I hae the normal 18-55mm lense that came with it, butI also have a Tamrn Pentax fit 80-210mm macro lense. I attatched it all fine, but now when I try to shoot the F keeps flashing and I cannot seem to fix it. Im sorry I sound so stupid, but i'm just trying to learn. Anyone know how to help?

enable ,,using aperture ring'' at custom menu
then

Set your camera to M mode using the mode dial (your camera won't fire in other modes*)
Compose and focus your image.
Using the aperture ring (the ring at the very back of your lens; it will have numbers such as 2.8, 4, 5.6, 8 written on it), select your desired aperture setting. Note that the smaller the aperture number is, the more light passes through the lens, and the blurrier the out of focus areas of your photograph will be.
[Screwmount lenses only] Switch the diaphragm clutch on your lens to "Manual" (you can leave it on Auto when composing and focusing).
Measure the light by either pressing the "Green Button", or pushing your power button to DOF preview mode (only available on select bodies). Your camera will automatically set the shutter speed for you.

All that's left now is for you to press the shutter release button to take your photo. Congratulations- you've now learned how to use M42 and M & K manual lenses with Pentax DSLRs!