hello, I have a question and I don`t know if here is the right place to be answered. How do I get the License of Mandriva Linux for installing in my school?

It is not, you should have started a new thread, and not in this forum which is dedicated to programming but in "Linux General" or perhaps "Linux / Linux Distributions / Mandriva".
A good guess would be from Mandriva web site.

Moved: This thread is more suitable in Mandriva and has been moved accordingly to help your thread/question get the exposure it deserves.

I don't know what license you are talking about. The free version of Mandriva is 100% FOSS software, meaning you are free to use it anywhere you want. I think you can install and use even the commercial products anywhere.

For educational use there are numerous special Linux's available, they include ADIOS, Skolelinux, Edubuntu, kmlinux, and so on.
Of course Mandriva is a good choice, but there is special stuff for schools. You may want to look at www.distrowatch.com and use their search function for details. Search for educational software.

We are open-source fans and believe in free software. As dexter11 pointed out, it is really free, no strings attached. Free as the spoken word, free as using the alphabet, free to be copied and passed-on legally!
Welcome to the world of free open-source and properly working software! If at some point in the future you feel you could contribute by developing software, good for you!