In other words, you downloaded an archive with Evolution inside ? Then that means you have to compile it. That means adapting the source code so that it can be adapted to your computer, and then actually install the configured program on your system.
I don't know if you're familiar with compiling programs, so here are the usual compilation steps : in the folder with the files from the archive, open a terminal and run :
- ./configure -> that will adapt the source code to your computer. In the end of the progress, you'll have an error message IF your computer lacks some elements to process with the next operation.
- make -> prepare the installation
- then, log as root (enter "su", and then provide admin's password)
- make install to install the program into your system
Another possibility is to download a package : it's an already preconfigured version adapted to your system, you can install it at once without the need of compiling it. That will be dependant on your distro.