Florence,
You put the code in a file named .htaccess located in the root directory of your web site – the same place where your WordPress files are located.
To deny access to a single IP address and allow everyone else, paste this code into your .htaccess file and change the 100.100.100.1 to the IP you want to block.
Order allow,deny
Deny from 100.100.100.1
Allow from all
You can create a .htaccess file with any text editor. Just open a blank text file and save it with the name .htaccess. Then FTP it to your site. Paste the blocking code in, change the IP address as needed, add more lines with “Deny from” and another IP, etc.
There are lots of other good uses for a .htaccess file and Google will give you links to tutorials and info.
Hope this helps,
-a-
