Hi Bisola
Welcome to the forums!
The first thing I would do if I were you would be to read through the install documentation very carefully.
http://www.zimbra.com/docs/ne/latest...erver_install/
It has most of everything you need there.
In a nutshell, basically you make sure nothing is currently listening on the web and mail ports on the server (such as Apache/postfix/sendmail, etc). If so, shut them down and disable them. Then grab the installer from the website, untar it, and run the setup file. The installer basically walks you through step by step.
Once the program is installed, you can access the admin interface of the program by visiting
https://yourserver.hostname.com:7071
If you run into problems, let us know and we can try to help out.
Good luck!