We want to get married?!?

Me and my boyfriend have just come up with the crazy idea of getting married lol..Been together a year and a half and he''s the only one for me..Wouldn't have a church wedding though,just a register office.How does this work?It says you have to pay 33.50 per person when you give notification of marriage then then another 43.50 fee with be payable on the day?Whats it mean?Thought it were very simple..I'm in the UK by the way.Thank you