Question:: What exactly is space and bandwidth/data transfer?
Answer:: Diskspace is the size your website can be. Every single letter on your website has to be stored somewhere on your web host's server. Each letter is one byte, and a megabyte is roughly one million bytes.
Bandwidth/Transfer is the amount of data the server will allow your site to send in a month. Transfer is usually measured in gigabytes - billions of bytes. Once you go over your monthly limit, a host may either shut your site down for the remainder of the month or it can charge you 'overage.'