If you ever spell a word wrong when typing in a URL, you're going to get a "Page cannot be found" error message. If you mess up capitalization and spacing, the same thing might happen.
You cannot use any spaces in an Internet address. It's just not the way URLs function. If you somehow hit the space bar while typing, you're not going to get to the Web site you're looking for. So, make sure you never use any spacing in a Web site's address.
Capitalization is a little different. Some Web sites may require capitalization. On the other hand, even though a URL has capital letters in it, you may still be directed to the site even if you use all lowercase letters. It all just depends on how the address is set up.
An Internet address only relies on case sensitive letters after the domain name. In other words, if you are ever trying to reach a page with some sort of a directory, you have to use all lowercase letters. For example, let's say you're wanting to visit Fred's Head. The URL is http://www.aph.org/fh/index.html. If you click this link you'll make it to the database. If you type the same URL in all caps: HTTP://WWW.APH.ORG/FH/INDEX.HTML you will receive an error.
If you were just going to the American Printing House for the Blind's homepage, you could type it either way, because it's not dealing with a directory and does not interfere with the domain name.
This rule also works the other way around. If a Web site's URL is all uppercase letters, typing it in lowercase would not work. If you're unsure about a site's address, try typing it in lowercase first, because the majority of URLs are set in lowercase letters. Very few sites actually make their address in all capital letters.