Once you have successfully compiled PowerShell, installing it is easy. All it takes is:
make install
This will install PowerShell in the directory you specified when you were configuring it (or /usr/local/bin if you didn't specify anything.)
At this point, if you wish, you can delete the whole directory containing the source for PowerShell.
Once PowerShell is installed, you can run it by typing /path/to/powershell (obviously, replace /path/to with the directory in which you installed it.) If the directory is in your current path (such as /usr/bin or possibly /usr/local/bin), you may just type powershell.