It depends.
If you're at 0.4.8, extract them into the keeperfx\levels folder, then in the 'free play levels' menu you will find the level listed below the deeper dungeons. Click to play. If you have a non-english language your translation may still be faulty and your 'free play levels' may be called something like 'deeper dungeons'. Described fully
here.
If you're at 0.4.9, extract them into the keeperfx\levels\[mappack] folder of your choice. I think in general picking 'classic' is best. Then navigate to the menu as described above, pick the mappack you put it in, and find it there.
Also, there's a discord with all of us, you're more than welcome to join:
https://discord.gg/zKTjfDh
It's a very convenient place to ask simple questions.