How does a booking number work? HELP!

Hi everyone, I've been slowly piecing together the production and theatre rental side to our show 'Boy Banned' and there suddenly arose an interesting point. How will we sell tickets? Now quite often I see a booking number on a poster for a show and I was wondering exactly how this works. We don't have credit card facilities...and tickets would only be really cheap so is it just used to put tickets aside? What kind of number should I use- a mobile or a home phone? What happens after someone has booked tickets? Do they pick them up on the night...and pay there? In general I guess (as it's my first time at this) I want to know how ticket booking numbers work so I can set one up for the show. Any help is AWESOME! Sean