Pauln90 has largely answered your question but it's important to note that certain channels aren't available to all Freeview viewers.
Firstly, some stations are transmitted using HD 'multiplexes' (which are 'bundles' of channels), even though the might not actually be broadcasting in HD. Such channels can only be received by Freeview sets that have actually got an HD tuner inside them, not just a standard definition tuner. (So the set needs to be a 'Freeview HD' one, not just a 'Freeview' one or an 'HD-ready Freeview' set).
Further, some specialist channels now need an internet connection to the TV as well which, in turn, means that only some (generally more recent) models of TV have the relevant technology inside them.
VisionTV (through which SpotlightTV can be received by some viewers) needs a Freeview HD set , not just an ordinary 'SD' Freeview one. Further, it needs to be one of the models in the list that can be accessed by clicking on the Freeview logo here:
https://www.visiontv.co.uk/#/where-to-watch
With loads of vastly different organisations (from mobile phone companies through to the emergency services and shipping) all wanting a share of the radio frequency spectrum, Freeview TV only has a very small number of frequencies allocated to it, meaning that only a limited number of channels can be accommodated. (That's why, for example, viewers in Scotland could no longer receive BBC 4 once BBC Scotland was launched. There's simply not enough room in the frequency spectrum for both channels to operate together). VisionTV tries to get around that problem by only using one Freeview channel itself but then feeding content from lots of other broadcasters onto viewers' screens via the internet.