Once you've determined which website you want to use, you need to visit their lair and hit the 'Sign up' button. You'll be invited to fill in personal details such as your name, address and telephone number. Then, you can pick your email address. Do be aware that most of the popular ones will be taken, but you should be able to find your full name if you're lucky.
Next, you'll be asked to type in some security questions that you will be able to answer if ever you should forget your password, which you'll also have to enter twice to guarantee it was typed in correctly. Typical questions you should use need to be things that you can remember easily, but others who may try to hack your account can't. For example, what was the name of your first pet, and what's your Mum's maiden name? Both of these are fantastic examples to help you get started.
It's very straightforward, and once you're on the website, it'll be very difficult to come into any more difficulty. If there are a few things that appear to be a little tricky though, don't forget to browse the Help pages or ask a friend who has a little more background knowledge in IT.