i m going to try block some website then i need to know its web host, but i do not know how to do, anyone expert please help. thanks.

http://vlaurie.com/computers2/Articles/hosts.htm

example:
102.54.94.97 rhino.acme.com
38.25.63.10 x.acme.com
127.0.0.1 localhost

Use NOTEPAD to open your hosts file. (There is no extention on the filename. (ie; .txt, .doc, etc. It's simply hosts.) In XP it's located at C:\WINDOWS\SYSTEM32\DRIVERS\ETC\.

When you open it, (if it hasn't been altered by any program yet) it will look like this;

# Copyright (c) 1993-1999 Microsoft Corp.
#
# This is a sample HOSTS file used by Microsoft TCP/IP for Windows.
#
# This file contains the mappings of IP addresses to host names. Each
# entry should be kept on an individual line. The IP address should
# be placed in the first column followed by the corresponding host name.
# The IP address and the host name should be separated by at least one
# space.
#
# Additionally, comments (such as these) may be inserted on individual
# lines or following the machine name denoted by a '#' symbol.
#
# For example:
#
# 102.54.94.97 rhino.acme.com # source server
# 38.25.63.10 x.acme.com # x client host

127.0.0.1 localhost

You would add the sites to your HOSTS file just under the 127.0.0.1 localhost line thus;
127.0.0.1 localhost
127.0.0.1 102.54.94.97 rhino.acme.com
127.0.0.1 38.25.63.10 x.acme.com
127.0.0.1 acestats.com
127.0.0.1 www.acestats.com
127.0.0.1 www.activesearch.com #[Adware.ActiveSearch]
127.0.0.1 actualnames.com #[Parasite.ActualNames][Spyware.ActualNames]
127.0.0.1 www.actualnames.com
127.0.0.1 ad-up.com
127.0.0.1 www.ad-up.com
127.0.0.1 adatom.com
127.0.0.1 aesp.adatom.com
127.0.0.1 adbest.com #[IE-SpyAd]
127.0.0.1 www.adcipta.net #[W32/Malware]
127.0.0.1 adserv.adbonus.com #[IE-SpyAd]
127.0.0.1 www.adbonus.com

When you're finished, close and save. Ensure no extention is added to the file name. If Notepad adds an extention, rename the file back to only hosts.

i want block www.punyu.com/puny/ , after enter its into noteped , it look no function. why?
127.0.0.1 www.punyu.com/puny/
127.0.0.1 punyu.com/puny/

is that correct ?

Get rid of the /puny/ - you want it to look like this: 127.0.0.1 www.punyu.com

I use and recommend HostsXpert. What is particularly nice about it is you can use it to merge the venerable MS MVP Hosts File into your own Hosts file. You can make backups, edit, flip back and forth between the fully populated hosts file and the MS default with ease - just about anything you like. Check it out.