How do people get 'Indefinite Leave To Enter' for the UK?

spouses of a UK citizen a granted a UK spouse visa for two years, after that period, the spouse is entitled to apply for ILR (which is permanent resicency in the UK), after spending one year as a ILR holder, the spouse is entitled to apply for British citizenship by naturalisation, to become a British citizen, one must have to p a test, and also the UKBA charge 735 British pounds as a fee to apply.