Before you can begin you must have jailbroken your iPhone. You can find instructions on how to do that for your device by using this chart.
Press to launch Cydia from your SpringBoard.
Press the Sections tab at the bottom right of the screen.
For this tutorial we will install Cyntact so lets choose Tweaks from the list of Sections.
Press to select Cyntact from the list of Packages. Notice that its in blue text to denote that its a paid app.
You will notice from the Package Details page that the application costs $1.00. If you would like to purchase it press the Purchase button at the top right of the screen.
You will be asked to login using your Facebook or your Google account. In this example I will choose Facebook.
If you already have a Facebook account press Log in to Cydia link at the bottom.
Enter your Facebook email and password then press Connect.
Once you have signed in successfully you will be brought to a Link Device page. From here click the Link Device to Your Account button.
You will now be brought to a Payments page. Cydia currently uses Amazon Payments but will support PayPal in the near future.
Press to select Pay $1.00 Now or Pay $1.00 Now and keep my information on file.
You will now be brought to the Amazon Payments page. Unfortunately, if you don't already have an account you will need to create one.
Enter your email address and password to sign into Amazon Payments.
From the Amazon Payments page choose your credit card or enter a new card number then press Continue.
You will be brought to a Payment Authorization page where you need to confirm the amount, card, and payee. The payment is made to SaurikIT, LLC.
Click the Confirm button to continue.
You will now see a transaction pending window. This window will update every 15 seconds as Amazon tries to process your credit card.
Once the payment has been made successfully you will see a Transaction Status of Success. Press the Close button at the top right of the screen to continue.
Notice we are back at the Package Details page for Cyntact. Instead of a purchase button at the top right we now have an Install button. You will also see the name of your account and a Package Officially Purchased message.
Press the Install button at the top right of the window.
Press the Confirm button at the top right of the window to begin installation.
Once the installation has completed successfully press the large Restart SpringBoard button.
You iPhone will now take you back to your SpringBoard and you can begin using your newly purchased application!