Go to PayPal.com and click the blue "Sign Up" button.
Choose the "Business Account" type.
Complete all required forms, click "Continue".
If everything is filled out correctly, your next step is to set up the account data (email, password, password restore questions).
PayPal will send you a confirmation letter to your email address.
Once you click the confirmation link you receive via email, your account goes live.
Go to https://developer.paypal.com.
Log in with your PayPal account data.
Choose "Dashboard" from the top menu.
Press "Create App" next to the "My REST apps" (you'll need an app to receive custom keys, but you don't have to do anything with it).
Fill out the "App name" field and press the "Create App" button (choose any name you like).
Awesome! Your app is live. Now click "Live credentials" and you will be presented with the payment data. You should copy information from the "Client ID" (Public key) and "Secret" (Private key) fields, and paste it into corresponding fields on your Parcl.com dashboard "Payment information" page.