Great lens. Did you get a lens hood with it? Some old lenses get a huge boost in IQ with a good lens hood.
For manual lenses you have to enable aperture ring usage in the menu and you're good to go. You can only shoot in M and Av mode. The way metering works depends on how "manual" the lens is. If the camera can operate its aperture, you can meter with the green button or shoot in Av mode (continuous metering, but will always be wide open). If your lens is a preset lens (you have to stop down by hand), then you can also shoot in Av and simply give the camera a second to meter with the lens stopped down and shoot. More info here:
https://www.pentaxforums.com/forums/pentax-lens-articles/110657-how-use-meter...k-x-k-7-a.html
Another great tool is catch in focus (also known as CiF and focus trapping). To do this, your lens has to short the AF contacts. You have to turn on AF on the camera and enable CiF in the menu, now you can just hold the shutter and the camera will fire when something is "in focus" (centre point). This can happen if something steps in front of the lens or if you slowly move the focus ring until something is in focus. You can also use burst mode here. Basically, this allows you to use the AF confirm on manual lenses.
To help with focusing, especially with old manual primes, you can read up on zone focusing and hyperfocal focusing. This can be a great technique when you know the approximate range where the subject will be or even for landscape photos.
Your camera also has focus peaking, you should enable it when you use fast primes. Liveview and focus peaking can be a big help with focusing.
And this is pretty much all I know. Have fun and be sure to post a couple "best of" photos in the critique section after you learn the ins and outs of the lens