These are the people that supply your website with somewhere to sit and be accessed from. They're often a wealth of information, so when you're trying to find your feet it will often be worthwhile to contact their tech support and get your questions answered. Because of this, it's important to contact them BEFORE you sign up for any packages to ensure that you'll receive a timely response. Just fire an email their way and see what happens.

This is the same as the space on your own PC's hard drive. Web Hosts will allocate a certain amount of space to your website, usually in Megabytes (MB) or gigabytes (GB). This determines how much you can store on your site.