Think of it as an electronic library with no control on the subject, quality or location of the books! Oh, and books may disappear at any time!
Addresses on the web look like http://site/path/file. The final file part may be omitted - a default file will be provided. When specified the file will probably end .htm or .html indicating it is a file with "HTML" layout commands in it. You will also find plain text files (.txt) and picture files (usually .gif or .jpg). Watch out for the tilde character "~" which often starts the path part.
You don't really need to know though ... once you have typed in one URL you can probably surf off round the world with only your mouse to guide you! For UK & Irish genealogy there is only one place to start - http://www.genuki.org.uk/
The GENUKI hierarchy consists of around 30 or 40 Megabytes (and growing) of information around the world (mostly in the UK) about UK & Irish genealogy plus a multitude of pointers off to other web sites of interest. Don't expect to find the data you want, however. It will be a long time (if ever) before you can use the internet as a substitute for a visit to your "ancestral record office". What you will find is a sprinkling of data and a wealth of information that will help with the groundwork you should do before the work "on the gound".
Here are some fast track entries into GENUKI:
Here is a better alternative to the soc.genealogy.surnames.* newsgroups ... instead of just reading the recent submissions (that's all usenet shows you) search the databse of all interests that have been submitted. There are two surnames databases available, one is a collection of all the postings to the surnames newsgroups, the other has a longer history and has a more specific submission procedure, it lists over 300000 interests from over 42000 people.
And here are some other pointers: