1. Login the admin dashboard of your Wordpress site, usually found at http://www.yourdomain.com/wp-admin/ (where yourdomain.com is your actual domain name)
2. Once in your dashboard, click Plugins from the left hand side.
3. In the Plugins sub menu, click Add New.
4. On the resulting page, type WPTouch into the Search field and click Search Plugins.
5. On the next page, you should have a list of search results. Find the result with the name WPTouch. Underneath that name, you will find "Details | Install Now". Click on Install Now.
6. Once installed, choose Settings from the left hand rail.
7. Click on the WPtouch submenu to customize your WPtouch settings.
Congratulations, you now have a mobile version of your Wordpress site.