Walk into a bank, or Building Society if you can find one, and say "I want a Mortgage". You are of course lying, nobody WANTS a mortgage. What you really mean is "I want to buy that house that I can't afford, so please give me lots of money so that I can spend the next 25 years of my life in penury".
Beware: saying " I want a mortgage" can induce mild hypertension in bank staff and they may offer to take you off to a small room and carry out strange initiation rites with you. Expect to hear about "The Mortgage Code" and "Appointed representatives", not to mention Indemnity Guarantees and Deposits.
Saying the same thing to an Estate Agent has much the same effect, but he/she will only take you to "the small room" in the hope that the "bank" will give them lots of the afore mentioned money for doing so.
Probably best to avoid the whole process and either win the Lottery or live in a tent.