How do I install and put Mani Admin Plugin on my server??

RTFM:
Easiest way is the VSP VDF method listed here http://www.mani-admin-plugin.com/index.p...&Itemid=25

The other way is with the MetaMod: Source server mod. There's instructions on the next page of that link to use MetaMod: Source as the base if you already have it installed, otherwise, it's kinda pointless.

Thank you, but I have another problem!
For my server i learned how to add a client, but Im having trouble add an admin and opening the menu!!
Please Help!

Again, RTFM:
This is now dependant on your version of Mani Admin. If you have the 1.2 beta, you can issue the commands, and if you're using v1.1, you need to edit the Adminlist.txt under the Mani_Admin_Plugin folder.

M: http://www.mani-admin-plugin.com/index.p...&Itemid=25

i added my name and steam ID to the clients.txt and when i launch my server and join it, i try to open the menu for admin but it always say that im not authorised.I can only do it in the console by rcon.

That's 1.2, and that's exactly what I said to do, run the commands, building the clients.txt is a bit much for a new server owner/admin. Take the easy route, then later once you have some more experience, take the hard route.