I got a new EV3 education kit.
Can I install it on a several computers or does the license work on one computer only?
That depends on which version of the Education Software you purchased:
If you're planning on installing this on more than three computers the Site License is the way to go.
Note that the Home Edition is a separate download, and would have it's own licensing, but appears to be freely available, and installable on as many computers as you like - details of some of the differences can be found in this answer to "What is different between the EV3 Home and Educational sets?".
In response to Alex's comment:
Without seeing the full wording of the license, it's hard to advise you correctly, however:
If you purchased the education set through First Lego League, you are allowed to install on up to 10 computers.
According to the license agreement supplied with the software (using the activation code from the Software Single License) you may:
a. use the Software on one single computer;
b. use the Software on a second computer as long as the first and second computers are not used simultaneously;
c. copy the Software for back-up and archival purposes, provided any copy made must contain all of the original Software’s proprietary notices;
So: You may install on more than 1 computer, but not use the software on more than 1 computer simultaneously.
You can reinstall the software after OS re-installation, as long as you have a backup copy of the software. According to the licence document (with the activation code), you can download the software only once. This seems not to be the case at the moment, but might change in the future.
You can install on a second computer, without removing it from the first. You are not allowed to use it on both computers at the same time, however.