First if you don't have a yahoo installer you need to open there official site. www.yahoomessenger.com and download yahoo messenger. Once you are already downloading you can now install yahoo messenger. Just follow the steps provide by the installer it is readable and easy to install.
Answers & Comments
First you need an internet connection
second you click on this link http://messenger.yahoo.com/
Click download and follow the steps
First if you don't have a yahoo installer you need to open there official site. www.yahoomessenger.com and download yahoo messenger. Once you are already downloading you can now install yahoo messenger. Just follow the steps provide by the installer it is readable and easy to install.