VISA & Border questions! Help!

1. I was scanning through the VISA (Tier 4) requirements and noticed that it says "...You can use the following documents to show that money is available to you: Personal bank or building society statements, covering a consecutive 28-day period ending no more than one month before the date of your application...". Now, I've never dealt with any bank statements or anything more complicated than taking the money out and putting it in. Can someone explain to me exactly what this means? It doesn't mean that I was supposed to have the funds in my bank account for the past 28 days.. does it?

2. Approximately how much money should I have in my bank account when crossing the border?

Please help!