If you want to sell low volumes of products on your website then using Paypal can work for you. If you have a single product then it is practical and quick and if you sell many then with a shopping cart integrated with your site and a PayPal business account you can be up and running quickly once your ecommerce website design is developed and live (or ready to go live.
Paypal step you through the process easily with this website and you can be up and running once you can verify a small payment to your account to prove you are a real business and person.
All you need is an email address and a bank account and following the steps above will have you up and running quickly.
Integrating the payment system with your websites means taking specific code snippets from the site for individual products and integrating with the PayPal system if you are using a specific eCommerce shopping cart. Your website developer should be able to help you with the details on this or you may wish to try it yourself.