If you already have a server then follow the installation instructions on the pterodactyl website. https://pterodactyl.io/panel/1.0/getting_started.html

Then if some step goes wrong:

if you want help you should provide detailed information. Tell exactly what commands you entered, from start to finish, not skipping anything and provide the outputs that you’ve gotten, especially the errors.

The pterodactyl discord will probably be more helpful there.