The customer portal is a great way for customers to be able to view their sales and quotes in one place, and to make payments on sales that have a balance due. Integrated credit card processing must be enabled for customer to make payments directly on their end.
The customer portal is enabled by default so there is nothing you need to do to add this feature. However here are a few tips you may want to consider to make the customer portal more customized and useful.
You can quickly access the customer portal from a sales order by clicking the options menu next to the customer and click Customer Portal:

When accessing the customer portal from a sales order, or if the customer clicks a link to the portal from an email they receive from OrderTrac (like the Payment Request email or just the default template for when emailing a sales order), the customer ID and name will already be filled in for them:

You can customize the background of this login screen by setting a Location Image in Settings > Location Settings > General tab. The logo displayed here will also be the logo set on the same location settings page.
The customer can click the Sales History option in the main menu to view all their quotes and sales. They can select a sales and if it has a balance due, they can click the Add Payment button to add a new credit card or gift card payment:

There are a few email templates you may want to update to enhance the usefulness of the customer portal and so the customer portal is easier to access by your customers.
The Sales order payment made from customer portal template will send you an email any time a customer makes a payment from the portal. You need to enable this template however. Click the template to open it, and make sure the Enabled radio is selected. You will also need to enter the email address that should receive these emails.

You can also update the Sales Order template, or any other template you regularly use when sending emails to customers, to include a link to the customer portal. You can add a little section indicating the customer can click the link below to visit the customer portal to view their sales and quote history, and to make payments. Then click the Customer Portal URL placeholder option to insert that placeholder into the template as shown below:

This way, when you email a customer their new sales order, it will already include a link to the customer portal so they have it for quick access. This link will be customized to that customer so the customer portal login page will already have their customer ID and name filled out.
The Payment Request template is also very useful with the customer portal. If you want the customer to make a payment, you can use this template when sending an email from the sales order. Go to the sales order, click the Email button to email the sales order to them:

Choose the Customer Copy and click next. Now you can choose the Payment Request template, and it will load below:

Click Send, and the customer will receive the email as shown above. This tells them they have a balance due and they can click the link to visit the customer portal to make a payment. Easy!
