From the Start menu, choose Programs, then Accessories, then "Command
Prompt". Or, using your preferred text editor, you can navigate to the hosts
file from the open dialog. Or you can navigate to it from within Explorer,
although you will then have to tell Explorer with what application you wish
to open the file.
FWIW, you can also alias domains you wish to block to 127.0.0.1, instead of
1.1.1.1. I believe that normally, 127.0.0.1 will "fail" to resolve the
request faster.