Signing up is optional, you can buy without it as well. In case, you would like to have an account, fill in sign up form, and press 'submit'.
Choose a brand or product type.
Choose an item, and press 'Add to Basket'.
Choose payment method, and press 'submit and continue'.
If you pay by Paypal, press 'I place the order, then I pay by Paypal'.
Press 'Pay now'.
Log in to your Paypal account and complete the process.