When you have selected the fonts you want to purchase and added them to your shopping cart, you can
review them there after selecting the "checkout" button in the main page.

After reading and accepting the Grixel Licence Agreement, click the "Proceed to Paypal" button and you will be taken to a secure page on Paypal's server.

You will notice that there is a padlock icon either in the url address field of the browser or on its status bar,and an "s" (for secure) after "http" in the url, meaning that you are in a secure page and the information that you are going to submit will only be visible to and kept at Paypal's server. If you notice that there is no "s" after the "https" word you must immediately stop your purchase process and restart from the top.
Two payment options are available from this page.
[1] You don't have a Paypal account but you have a credit card
[2] You have a Paypal account
Let's see the first case,
You don't have a Paypal account but you have a credit card
after clicking the [1] button, you will be taken to the folowing page:

Here you must fill all the fields that are necessary for Paypal (the ones with the red asterisk).
Fields City, Address and Home Telephone are only needed for Paypal's records, and not for the actual purchase of the fonts.
I cannot see any of the information you give to Paypal and that is what Paypal is able to do. You authorise Paypal to charge your credit card with the amount due for the fonts purchased, and I will be informed by Paypal that you have paid them for my fonts, without ever knowing what credit card you used to pay for them.
Clicking on the "Continue" button you will be taken to the next page:

where you can review your billing information once again, while still being able to edit it. If everything is ok click "Pay" ...

and your purchase will be completed.
The "Sign Up" button is for becoming a Paypal member thus obtaining a Paypal account. Give a password you want to have with your paypal account and press Sign Up.

This has many advantages, as once you become a member, you will no longer have to retype your credit card information in a purchase process for a site that accepts payments by Paypal, but only your email and Paypal's password.
The "Return to Merchant" button will lead you back to Grixel website meaning that everything was completed succesfully.
Now let's see case [2]:
You have a Paypal account

Login with your email and Paypal's password, then click the [2] button...

and you are ready to " Pay".?No credit card information is needed, as (only) Paypal already has it on file.

The "View your printable receipt" button will open you a popup from where you can do what it says:

The "Return to Merchant" button will lead you back to Grixel website meaning that everything was completed succesfully.
Because, in both cases above, you are leaving from a secure page (Paypal) and going to a non secure (Grixel) a pop up alert may come up warning you:

but you don't have to worry about it, as it is for information purposes only, explaining that you are leaving an encrypted webpage. All the billing information is already given in previous pages and there is no need for personal information from now on. Just click "Continue".

If you see the above web page, it means that the purchase process is completed, and it is time for you to check your email for download parameters. Immediate download is now available.