The recorder will be similar to a VCR in its set up.
That is it will have its own inbuilt tuner
So that it will record any program you set it to from the normal terrestrial source.
It will also record from an external 'Box'
This will be denoted with the 'L' prefix on screen.
So it will record BBC 1&2 ITV Ch4 Ch5 then series of 'L' numbers which will accord to the 'External Box inputs.
So to record from your Sky box you set up the Sky box to come on at the set time
Then you set the recorder to ditto but set to the appropriate 'L' channel per the manual.