K-mount lenses on DSLR

I wonder if anyone here can help.

I have just bought a Pentax K1000D.

One of my reasons for buying it was that I have several old K-mount lenses, and the spec. states that these can be used, albeit "with restrictions".

I can't get them to work at all. No useful information comes up on the display, and the shutter won't move. I can't find anything in the manual to help me.

Does anyone know whether there is a specific setting that I need to use? Alternatively, do I need some sort of adaptor?

Thanks in advance for any info or ideas.

William