The channels are broadcast in the range of 950MHz to 2150MHz. The LNB shifts these frequencies into something that can be passed down the co-axial wire. It does this in two 'chunks' (hence the low and high oscillator markings and that 22kHz tone stuff).
The LNB does not actually 'tune' to anything. It receives everything within a range of frequencies. The best way to imagine this is to compare it against a normal metal TV antenna. It receives 'everything' in much the same way.
There is a small further complication. Polarity. The best thing to do, if you don't understand, is to ignore it. Arranging the transponders on alternate polarities (H, V, H, V...) is basically a way to squash the transponders closer together - frequency-wise - without having adjacent channels interfere with each other.
The tuner pictured is a ZIF style tuner as fitted into various Pace digital receivers. On the right is an inverted close-up of the IC on the tuner board.
For those of us overseas, it is useful to know what satellite receivers are better suited to 'fringe' area reception.
The following recommendations are not my own - I have trawled various on-line documents and newgroups. If you have anything to add, please let me know...