Your host likely has a 1-click installer that you can use to easily install Joomla, if not, follow the instructions as given by them directly: http://docs.joomla.org/Installation
now joomla installation is really easy . just upload .tar file of joomla installation and then try to install , its really easy
I would not use the Fantastico method of installing. Normal installation as mentioned above is better. Good luck.
First, you have to figure out what version of Joomla you're going to install. If it is Joomla 1.5, I suggest you to install 2.5 instead because Joomla will no longer support Joomla 1.5 soon. About the steps, you can find it eassily in Joomla! Document: docs.joomla.org/Installing_Joomla!
I wouldn't use your hosting companies one step install, I once tried it, and couldn't even change the template, because they said it posed a security threat.