well i have cron job in my cpanel i like to know how i should add the code (25 * * * * curl --user login:pass http://zyx.com/blog/wp-content/update-feeds.php -d update=quiet ) which is given in the manual
I can tell you what it means, but I don't know what your panel looks like as I've not used CPanel before. So you'll have to figure that part out yourself.
cron directives look like this:
25 * * * * command
The number and each of those asterisks define when the job runs. It goes like this:
day of month
day of week
So the job you've posted says to run the command once every hour, on the 25th minute. So at 1:25, 2:25, 3:25, etc.
Now, the command you gave was this:
curl --user login:pass http://zyx.com/blog/wp-content/update-feeds.php -d update=quiet
curl is like a command line http client. That's basically a command to retrieve that URL.
So, every hour, your cron job will go and get that URL, which causes the update-feeds.php script to run.
You don't have to use curl. wget or lynx will work just as well for a cron job. You'll really probably want to ask your host how to do that command correctly, because it'll vary depending on their system and such. Then just set it to run however often you like. My email posting command (using Postie) runs every 15 minutes, for example. How often is up to you, what the command is depends on your host.