You must have an installation of pterodactyl with an admin account. Learn more here
Installing eggactyl is a fairly easy process.
Download the egg.json from here.Open your pterodactyl admin panel.
Go to nests, and click on the "Create New" button.
In the name, type eggactyl and press "Save".
Now, Go back to Nests, and click on "Import Egg".
Select the egg.json you downloaded earlier, and Set the associated Nest to pterodactyl.