Could you PLEASE explain in PLAIN ENGLISH how to do this?

One way is to change your hosts file as I explained in either this thread or the "2345" thread - I don't remember which now...

On Windows the file is here:
C:\windows\System32\drivers\etc\hosts

You can edit it with notepad - add the following lines to the end:
127.0.0.1 www.2345.com
127.0.0.1 2345.com

... for any other site you want to block, do similar

127.0.0.1 www.bad.malware.site

The file downloadable from http://winhelp2002.mvps.org/ is a huge file to replace your hosts file, containing similar entries for several thousand malware and adware sites. Actually it doesn't currently include 2345.com, but it's easy enough to add more to the list as described above.

On Mac OS X, Linux or other Unix-like systems, the same file is at
/etc/hosts